1.
Combustion
–
Combustion in a fire produces a flame, and the heat produced can make combustion self-sustaining. Combustion is often a sequence of elementary radical reactions. Solid fuels, such as wood, first undergo endothermic pyrolysis to produce gaseous fuels whose combustion then supplies the required to produce more of them. Combustion is often hot enough that light in the form of either glowing or a flame is produced, a simple example can be seen in the combustion of hydrogen and oxygen into water vapor, a reaction commonly used to fuel rocket engines. The bond energies in the play only a minor role, since they are similar to those in the combustion products. The heat of combustion is approximately -418 kJ per mole of O2 used up in the combustion reaction, uncatalyzed combustion in air requires fairly high temperatures. Complete combustion is stoichiometric with respect to the fuel, where there is no remaining fuel, thermodynamically, the chemical equilibrium of combustion in air is overwhelmingly on the side of the products. Thus, the smoke is usually toxic and contains unburned or partially oxidized products. Since combustion is rarely clean, flue gas cleaning or catalytic converters may be required by law, fires occur naturally, ignited by lightning strikes or by volcanic products. Combustion was the first controlled chemical reaction discovered by humans, in the form of campfires and bonfires, usually, the fuel is carbon, hydrocarbons or more complicated mixtures such as wood that contains partially oxidized hydrocarbons. Combustion is also currently the only used to power rockets. Combustion is also used to destroy waste, both nonhazardous and hazardous, oxidants for combustion have high oxidation potential and include atmospheric or pure oxygen, chlorine, fluorine, chlorine trifluoride, nitrous oxide and nitric acid. For instance, hydrogen burns in chlorine to form hydrogen chloride with the liberation of heat, although usually not catalyzed, combustion can be catalyzed by platinum or vanadium, as in the contact process. In complete combustion, the reactant burns in oxygen, producing a number of products. When a hydrocarbon burns in oxygen, the reaction will yield carbon dioxide. When elements are burned, the products are primarily the most common oxides, carbon will yield carbon dioxide, sulfur will yield sulfur dioxide, and iron will yield iron oxide. Nitrogen is not considered to be a combustible substance when oxygen is the oxidant, Combustion is not necessarily favorable to the maximum degree of oxidation, and it can be temperature-dependent. For example, sulfur trioxide is not produced quantitatively by the combustion of sulfur, NOx species appear in significant amounts above about 2,800 °F, and more is produced at higher temperatures
2.
Reagent
–
A reagent /riˈeɪdʒənt/ is a substance or compound added to a system to cause a chemical reaction, or added to test if a reaction occurs. The terms reactant and reagent are often used interchangeably—however, a reactant is more specifically a substance consumed in the course of a chemical reaction, solvents, though involved in the reaction, are usually not called reactants. Similarly, catalysts are not consumed by the reaction, so they are not reactants, in biochemistry, especially in connection with enzyme-catalyzed reactions, the reactants are commonly called substrates. In organic chemistry, the term reagent denotes a chemical ingredient introduced to cause a transformation of an organic substance. Examples include the Collins reagent, Fentons reagent, and Grignard reagents, examples include Fehlings reagent, Millons reagent, and Tollens reagent. Purity standards for reagents are set by such as ASTM International or the American Chemical Society. For instance, reagent-quality water must have low levels of impurities such as sodium and chloride ions, silica. Laboratory products which are pure, but still useful and economical for undemanding work, may be designated as technical, practical. In the field of biology, the revolution in the 1980s grew from the development of reagents that could be used to identify and manipulate the chemical matter in. These reagents included antibodies, oligomers, all sorts of organisms and immortalised cell lines, reagents and methods for molecular cloning and DNA replication
3.
Product (chemistry)
–
Products are the species formed from chemical reactions. During a chemical reaction reactants are transformed into products after passing through an energy transition state. This process results in the consumption of the reactants, when represented in chemical equations products are by convention drawn on the right-hand side, even in the case of reversible reactions. The properties of such as their energies help determine several characteristics of a chemical reaction such as whether the reaction is exergonic or endergonic. Additionally the properties of a product can make it easier to extract and purify following a chemical reaction, reactants are molecular materials used to create chemical reactions. The atoms arent created or destroyed, the materials are reactive and reactants are rearranging during a chemical reaction. Here is an example of reactants, CH4 + O2, a non-example is CO2 + H2O or energy. Much of chemistry research is focused on the synthesis and characterization of beneficial products, as well as the detection, other fields include natural product chemists who isolate products created by living organisms and then characterize and study these products. The products of a chemical reaction influence several aspects of the reaction, if the products are lower in energy than the reactants, then the reaction will give off excess energy making it an exergonic reaction. Such reactions are thermodynamically favorable and tend to happen on their own, if the kinetics of the reaction are high enough, however, then the reaction may occur too slowly to be observed, or not even occur at all. If the products are higher in energy than the reactants then the reaction will require energy to be performed and is therefore an endergonic reaction. Additionally if the product is less stable than a reactant, then Lefflers assumption holds that the state will more closely resemble the product than the reactant. Ever since the mid nineteenth century chemists have been preoccupied with synthesizing chemical products. Much of synthetic chemistry is concerned with the synthesis of new chemicals as occurs in the design and creation of new drugs, in biochemistry, enzymes act as biological catalysts to convert substrate to product. For example, the products of the enzyme lactase are galactose and glucose, S + E → P + E Where S is substrate, P is product and E is enzyme. Some enzymes display a form of promiscuity where they convert a single substrate into multiple different products and it occurs when the reaction occurs via a high energy transition state that can be resolved into a variety of different chemical products. Some enzymes are inhibited by the product of their reaction binds to the enzyme and this can be important in the regulation of metabolism as a form of negative feedback controlling metabolic pathways. Product inhibition is also an important topic in biotechnology, as overcoming this effect can increase the yield of a product, Chemical reaction Substrate Reagent Precursor Catalyst Enzyme Product Derivative Chemical equilibrium Second law of thermodynamics
4.
Chemical reaction
–
A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Nuclear chemistry is a sub-discipline of chemistry that involves the reactions of unstable. The substance initially involved in a reaction are called reactants or reagents. Chemical reactions are characterized by a chemical change, and they yield one or more products. Reactions often consist of a sequence of individual sub-steps, the elementary reactions. Chemical reactions are described with chemical equations, which present the starting materials, end products. Chemical reactions happen at a characteristic reaction rate at a given temperature, typically, reaction rates increase with increasing temperature because there is more thermal energy available to reach the activation energy necessary for breaking bonds between atoms. Reactions may proceed in the forward or reverse direction until they go to completion or reach equilibrium, Reactions that proceed in the forward direction to approach equilibrium are often described as spontaneous, requiring no input of free energy to go forward. Non-spontaneous reactions require input of energy to go forward. Different chemical reactions are used in combinations during chemical synthesis in order to obtain a desired product, in biochemistry, a consecutive series of chemical reactions form metabolic pathways. These reactions are catalyzed by protein enzymes. Chemical reactions such as combustion in fire, fermentation and the reduction of ores to metals were known since antiquity, in the Middle Ages, chemical transformations were studied by Alchemists. They attempted, in particular, to lead into gold, for which purpose they used reactions of lead. The process involved heating of sulfate and nitrate minerals such as sulfate, alum. In the 17th century, Johann Rudolph Glauber produced hydrochloric acid and sodium sulfate by reacting sulfuric acid, further optimization of sulfuric acid technology resulted in the contact process in the 1880s, and the Haber process was developed in 1909–1910 for ammonia synthesis. From the 16th century, researchers including Jan Baptist van Helmont, Robert Boyle, the phlogiston theory was proposed in 1667 by Johann Joachim Becher. It postulated the existence of an element called phlogiston, which was contained within combustible bodies. This proved to be false in 1785 by Antoine Lavoisier who found the explanation of the combustion as reaction with oxygen from the air
5.
Conservation of mass
–
Hence, the quantity of mass is conserved over time. Thus, during any chemical reaction, nuclear reaction, or radioactive decay in an isolated system, the concept of mass conservation is widely used in many fields such as chemistry, mechanics, and fluid dynamics. e. Those completely isolated from all exchanges with the environment, in this circumstance, the mass–energy equivalence theorem states that mass conservation is equivalent to total energy conservation, which is the first law of thermodynamics. By contrast, for a closed system mass is only approximately conserved. Certain types of matter may be created or destroyed, but in all of these processes, for a discussion, see mass in general relativity. An important idea in ancient Greek philosophy was that Nothing comes from nothing, so that what exists now has always existed, no new matter can come into existence where there was none before. A further principle of conservation was stated by Epicurus who, describing the nature of the Universe, wrote that the totality of things was always such as it is now, and always will be. Jain philosophy, a non-creationist philosophy based on the teachings of Mahavira, states that the universe, the Jain text Tattvarthasutra states that a substance is permanent, but its modes are characterised by creation and destruction. A principle of the conservation of matter was also stated by Nasīr al-Dīn al-Tūsī and he wrote that A body of matter cannot disappear completely. It only changes its form, condition, composition, color and other properties, the principle of conservation of mass was first outlined by Mikhail Lomonosov in 1748. He proved it by experiments—though this is sometimes challenged, antoine Lavoisier had expressed these ideas in 1774. Others whose ideas pre-dated the work of Lavoisier include Joseph Black, Henry Cavendish, the conservation of mass was obscure for millennia because of the buoyancy effect of the Earths atmosphere on the weight of gases. For example, a piece of wood weighs less after burning, the vacuum pump also enabled the weighing of gases using scales. Once understood, the conservation of mass was of importance in progressing from alchemy to modern chemistry. His research indicated that in certain reactions the loss or gain could not have more than from 2 to 4 parts in 100,000. The difference in the accuracy aimed at and attained by Lavoisier on the one hand, in special relativity, the conservation of mass does not apply if the system is open and energy escapes. However, it continue to apply to totally closed systems. If energy cannot escape a system, its mass cannot decrease, in relativity theory, so long as any type of energy is retained within a system, this energy exhibits mass
6.
Oxygen
–
Oxygen is a chemical element with symbol O and atomic number 8. It is a member of the group on the periodic table and is a highly reactive nonmetal. By mass, oxygen is the third-most abundant element in the universe, after hydrogen, at standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula O2. This is an important part of the atmosphere and diatomic oxygen gas constitutes 20. 8% of the Earths atmosphere, additionally, as oxides the element makes up almost half of the Earths crust. Most of the mass of living organisms is oxygen as a component of water, conversely, oxygen is continuously replenished by photosynthesis, which uses the energy of sunlight to produce oxygen from water and carbon dioxide. Oxygen is too reactive to remain a free element in air without being continuously replenished by the photosynthetic action of living organisms. Another form of oxygen, ozone, strongly absorbs ultraviolet UVB radiation, but ozone is a pollutant near the surface where it is a by-product of smog. At low earth orbit altitudes, sufficient atomic oxygen is present to cause corrosion of spacecraft, the name oxygen was coined in 1777 by Antoine Lavoisier, whose experiments with oxygen helped to discredit the then-popular phlogiston theory of combustion and corrosion. One of the first known experiments on the relationship between combustion and air was conducted by the 2nd century BCE Greek writer on mechanics, Philo of Byzantium. In his work Pneumatica, Philo observed that inverting a vessel over a burning candle, Philo incorrectly surmised that parts of the air in the vessel were converted into the classical element fire and thus were able to escape through pores in the glass. Many centuries later Leonardo da Vinci built on Philos work by observing that a portion of air is consumed during combustion and respiration, Oxygen was discovered by the Polish alchemist Sendivogius, who considered it the philosophers stone. In the late 17th century, Robert Boyle proved that air is necessary for combustion, English chemist John Mayow refined this work by showing that fire requires only a part of air that he called spiritus nitroaereus. From this he surmised that nitroaereus is consumed in both respiration and combustion, Mayow observed that antimony increased in weight when heated, and inferred that the nitroaereus must have combined with it. Accounts of these and other experiments and ideas were published in 1668 in his work Tractatus duo in the tract De respiratione. Robert Hooke, Ole Borch, Mikhail Lomonosov, and Pierre Bayen all produced oxygen in experiments in the 17th and the 18th century but none of them recognized it as a chemical element. This may have been in part due to the prevalence of the philosophy of combustion and corrosion called the phlogiston theory, which was then the favored explanation of those processes. Established in 1667 by the German alchemist J. J. Becher, one part, called phlogiston, was given off when the substance containing it was burned, while the dephlogisticated part was thought to be its true form, or calx. The fact that a substance like wood gains overall weight in burning was hidden by the buoyancy of the combustion products
7.
Properties of water
–
Water is a polar inorganic compound that is at room temperature a tasteless and odorless liquid, nearly colorless with a hint of blue. This simplest hydrogen chalcogenide is by far the most studied chemical compound and is described as the solvent for its ability to dissolve many substances. This allows it to be the solvent of life and it is the only common substance to exist as a solid, liquid, and gas in nature. Water molecules form hydrogen bonds with other and are strongly polar. This polarity allows it to separate ions in salts and strongly bond to other substances such as alcohols and acids. Water is amphoteric, meaning it is both an acid and a base—it produces H+ and OH− ions by self ionization and this regulates the concentrations of H+ and OH− ions in water. Due to water being a good solvent, it is rarely pure. However, there are many compounds that are essentially, if not completely, insoluble in water, such as fats, oils. The accepted IUPAC name of water is oxidane or simply water, or its equivalent in different languages, oxidane is only intended to be used as the name of the mononuclear parent hydride used for naming derivatives of water by substituent nomenclature. These derivatives commonly have other recommended names, for example, the name hydroxyl is recommended over oxidanyl for the –OH group. The name oxane is explicitly mentioned by the IUPAC as being unsuitable for this purpose, the simplest systematic name of water is hydrogen oxide. This is analogous to related compounds such as hydrogen peroxide, hydrogen sulfide, the polarized form of the water molecule, H+OH−, is also called hydron hydroxide by IUPAC nomenclature. It is a rarely used name of water, and mostly used in various hoaxes or spoofs that call for this chemical to be banned. Other systematic names for water include hydroxic acid, hydroxylic acid, none of these exotic names are used widely. Water is the substance with chemical formula H 2O, one molecule of water has two hydrogen atoms covalently bonded to a single oxygen atom. Water is a tasteless, odorless liquid at ambient temperature and pressure, ice also appears colorless, and water vapor is essentially invisible as a gas. The elements surrounding oxygen in the table, nitrogen, fluorine, phosphorus, sulfur and chlorine. The reason that water forms a liquid is that oxygen is more electronegative than all of elements with the exception of fluorine
8.
Ideal gas
–
An ideal gas is a theoretical gas composed of many randomly moving point particles whose only interaction is perfectly elastic collision. The ideal gas concept is useful because it obeys the ideal gas law, an equation of state. One mole of a gas has a volume of 22.710947 litres at STP as defined by IUPAC since 1982. At normal conditions such as temperature and pressure, most real gases behave qualitatively like an ideal gas. Many gases such as nitrogen, oxygen, hydrogen, noble gases, the ideal gas model tends to fail at lower temperatures or higher pressures, when intermolecular forces and molecular size become important. It also fails for most heavy gases, such as many refrigerants, at high pressures, the volume of a real gas is often considerably greater than that of an ideal gas. At low temperatures, the pressure of a gas is often considerably less than that of an ideal gas. At some point of low temperature and high pressure, real gases undergo a phase transition, the model of an ideal gas, however, does not describe or allow phase transitions. These must be modeled by more complex equations of state, the deviation from the ideal gas behaviour can be described by a dimensionless quantity, the compressibility factor, Z. The ideal gas model has been explored in both the Newtonian dynamics and in quantum mechanics, the ideal gas model has also been used to model the behavior of electrons in a metal, and it is one of the most important models in statistical mechanics. There are three classes of ideal gas, the classical or Maxwell–Boltzmann ideal gas, the ideal quantum Bose gas, composed of bosons. The classical ideal gas can be separated into two types, The classical thermodynamic ideal gas and the ideal quantum Boltzmann gas. The ideal quantum Boltzmann gas overcomes this limitation by taking the limit of the quantum Bose gas, the behavior of a quantum Boltzmann gas is the same as that of a classical ideal gas except for the specification of these constants. The ideal gas law is an extension of experimentally discovered gas laws, real fluids at low density and high temperature approximate the behavior of a classical ideal gas. This deviation is expressed as a compressibility factor, the classical thermodynamic properties of an ideal gas can be described by two equations of state. Multiplying the equations representing the three laws, V ∗ V ∗ V = k b a Gives, V ∗ V ∗ V =, under ideal conditions, V = R, that is, P V = n R T. The other equation of state of an ideal gas must express Joules law, in order to switch from macroscopic quantities to microscopic ones, we use n R = N k B where N is the number of gas particles kB is the Boltzmann constant. The probability distribution of particles by velocity or energy is given by the Maxwell speed distribution, the assumption of spherical particles is necessary so that there are no rotational modes allowed, unlike in a diatomic gas
9.
Ideal gas law
–
The ideal gas law is the equation of state of a hypothetical ideal gas. It is an approximation of the behavior of many gases under many conditions. It was first stated by Émile Clapeyron in 1834 as a combination of the empirical Boyles law, Charless law and it can also be derived microscopically from kinetic theory, as was achieved by August Krönig in 1856 and Rudolf Clausius in 1857. The state of an amount of gas is determined by its pressure, volume, the modern form of the equation relates these simply in two main forms. The temperature used in the equation of state is an absolute temperature, in SI units, P is measured in pascals, V is measured in cubic metres, n is measured in moles, and T in kelvins. R has the value 8.314 J/ ≈2 cal/, how much gas is present could be specified by giving the mass instead of the chemical amount of gas. Therefore, a form of the ideal gas law may be useful. The chemical amount is equal to the mass of the gas divided by the molar mass. By replacing n with m/M and subsequently introducing density ρ = m/V, we get, defining the specific gas constant Rspecific as the ratio R/M, P = ρ R specific T. This form of the gas law is very useful because it links pressure, density. Alternatively, the law may be written in terms of the specific volume v and it is common, especially in engineering applications, to represent the specific gas constant by the symbol R. In such cases, the gas constant is usually given a different symbol such as R ¯ to distinguish it. In any case, the context and/or units of the gas constant should make it clear as to whether the universal or specific gas constant is being referred to. KB =R/NA The number density contrasts to the formulation, which uses n, the number of moles and V. This relation implies that R = NAkB, where NA is Avogadros constant, in extreme conditions the principles of statistical mechanics may break down as some of the assumptions relating a real life example to an ideal gas become untrue. In SI units, P is measured in pascals, V in cubic metres, Y is a dimensionless number, KB has the value 1. 38·10−23 J/K in SI units. According to the assumptions of the theory of gases, we assumed that there are no inter molecular attractions between the molecules of an ideal gas its potential energy is zero. Hence, all the energy possessed by the gas is kinetic energy, E =32 R T This is the kinetic energy of one mole of a gas
10.
Isotope
–
Isotopes are variants of a particular chemical element which differ in neutron number. All isotopes of an element have the same number of protons in each atom. The number of protons within the nucleus is called atomic number and is equal to the number of electrons in the neutral atom. Each atomic number identifies a specific element, but not the isotope, the number of nucleons in the nucleus is the atoms mass number, and each isotope of a given element has a different mass number. For example, carbon-12, carbon-13 and carbon-14 are three isotopes of the element carbon with mass numbers 12,13 and 14 respectively. The atomic number of carbon is 6, which means that carbon atom has 6 protons. Nuclide refers to a rather than to an atom. Identical nuclei belong to one nuclide, for each nucleus of the carbon-13 nuclide is composed of 6 protons and 7 neutrons. The nuclide concept emphasizes nuclear properties over chemical properties, whereas the isotope concept emphasizes chemical over nuclear, the neutron number has large effects on nuclear properties, but its effect on chemical properties is negligible for most elements. Because isotope is the term, it is better known than nuclide. An isotope and/or nuclide is specified by the name of the particular element followed by a hyphen, when a chemical symbol is used, e. g. C for carbon, standard notation is to indicate the number with a superscript at the upper left of the chemical symbol. Because the atomic number is given by the element symbol, it is common to only the mass number in the superscript. The letter m is sometimes appended after the number to indicate a nuclear isomer. For example, 14C is a form of carbon, whereas 12C. There are about 339 naturally occurring nuclides on Earth, of which 286 are primordial nuclides, primordial nuclides include 32 nuclides with very long half-lives and 254 that are formally considered as stable nuclides, because they have not been observed to decay. In most cases, for reasons, if an element has stable isotopes. Theory predicts that many apparently stable isotopes/nuclides are radioactive, with extremely long half-lives, of the 254 nuclides never observed to decay, only 90 of these are theoretically stable to all known forms of decay
11.
Jeremias Benjamin Richter
–
Jeremias Benjamin Richter was a German chemist. He is known for introducing the term stoichiometry, evidence for the existence of atoms was the law of definite proportions proposed by him in 1792. Richter found that the ratio by weight of the compounds consumed in a reaction was always the same. It took 615 parts by weight of magnesia, for example, from his data, Ernst Gottfried Fischer calculated in 1802 the first table of chemical equivalents, taking sulphuric acid as the standard with the figure 1000. When Joseph Proust reported his work on the constant composition of chemical compounds, between 1792 and 1794 he published a three-volume summary of his work on the law of definite proportions. Richter was fascinated with the role of mathematics in chemistry, unfortunately his writing style has been described as obscure and clumsy. His work therefore had little impact until 1802, when it was summarized by Ernst Gottfried Fischer in terms of tables, attribution Chisholm, Hugh, ed. Richter, Jeremias Benjamin
12.
Ancient Greek
–
Ancient Greek includes the forms of Greek used in ancient Greece and the ancient world from around the 9th century BC to the 6th century AD. It is often divided into the Archaic period, Classical period. It is antedated in the second millennium BC by Mycenaean Greek, the language of the Hellenistic phase is known as Koine. Koine is regarded as a historical stage of its own, although in its earliest form it closely resembled Attic Greek. Prior to the Koine period, Greek of the classic and earlier periods included several regional dialects, Ancient Greek was the language of Homer and of fifth-century Athenian historians, playwrights, and philosophers. It has contributed many words to English vocabulary and has been a subject of study in educational institutions of the Western world since the Renaissance. This article primarily contains information about the Epic and Classical phases of the language, Ancient Greek was a pluricentric language, divided into many dialects. The main dialect groups are Attic and Ionic, Aeolic, Arcadocypriot, some dialects are found in standardized literary forms used in literature, while others are attested only in inscriptions. There are also several historical forms, homeric Greek is a literary form of Archaic Greek used in the epic poems, the Iliad and Odyssey, and in later poems by other authors. Homeric Greek had significant differences in grammar and pronunciation from Classical Attic, the origins, early form and development of the Hellenic language family are not well understood because of a lack of contemporaneous evidence. Several theories exist about what Hellenic dialect groups may have existed between the divergence of early Greek-like speech from the common Proto-Indo-European language and the Classical period and they have the same general outline, but differ in some of the detail. The invasion would not be Dorian unless the invaders had some relationship to the historical Dorians. The invasion is known to have displaced population to the later Attic-Ionic regions, the Greeks of this period believed there were three major divisions of all Greek people—Dorians, Aeolians, and Ionians, each with their own defining and distinctive dialects. Often non-west is called East Greek, Arcadocypriot apparently descended more closely from the Mycenaean Greek of the Bronze Age. Boeotian had come under a strong Northwest Greek influence, and can in some respects be considered a transitional dialect, thessalian likewise had come under Northwest Greek influence, though to a lesser degree. Most of the dialect sub-groups listed above had further subdivisions, generally equivalent to a city-state and its surrounding territory, Doric notably had several intermediate divisions as well, into Island Doric, Southern Peloponnesus Doric, and Northern Peloponnesus Doric. The Lesbian dialect was Aeolic Greek and this dialect slowly replaced most of the older dialects, although Doric dialect has survived in the Tsakonian language, which is spoken in the region of modern Sparta. Doric has also passed down its aorist terminations into most verbs of Demotic Greek, by about the 6th century AD, the Koine had slowly metamorphosized into Medieval Greek
13.
Nikephoros I of Constantinople
–
St. Nikephoros I or Nicephorus I, was a Christian Byzantine writer and Ecumenical Patriarch of Constantinople from April 12,806, to March 13,815. He was born in Constantinople as the son of Theodore and Eudokia, of an orthodox family. Nevertheless, he entered the service of the Empire, became cabinet secretary and he then withdrew to one of the cloisters that he had founded on the eastern shore of the Bosporus, until he was appointed director of the largest home for the destitute in Constantinople c. After the death of the Patriarch Tarasios, although still a layman, after vain theological disputes, in December 814, there followed personal insults. From there he carried on a literary polemic for the cause of the iconodules against the synod of 815, on the occasion of the change of emperors, in 820, he was put forward as a candidate for the patriarchate and at least obtained the promise of toleration. He died at the monastery of Saint Theodore, revered as a confessor and his feast is celebrated on this day both in the Greek and Roman Churches, the Greeks also observe 2 June as the day of his death. He was mild in his ecclesiastical and monastical rules and non-partisan in his treatment of the period from 602 to 769. He used the chronicle of Traianus Patricius, the Chronography offered a universal history from the time of Adam and Eve to his own time. To it he appended a canon catalog, the catalog of the accepted books of the Old and New Testaments is followed by the antilegomena and the apocrypha. Next to each book is the count of its lines, his stichometry, to which we can compare our accepted texts and this is especially useful for apocrypha for which only fragmentary texts have survived. Nikephoros follows in the path of John of Damascus, list of Catholic saints The Oxford Dictionary of Byzantium, Oxford University Press,1991. Paul J. Alexander, The Patriarch Nicephorus of Constantinople, Oxford University Press,1958, development of the Canon of the New Testament, the Stichometry of Nicephorus St. Nicephorus
14.
Biblical canon
–
A biblical canon or canon of scripture is a list of texts which a particular religious community regards as authoritative scripture. The word canon comes from the Greek κανών, meaning rule or measuring stick, Christians became the first to use the term in reference to scripture, but Eugene Ulrich regards the idea as Jewish. In contrast, a canon, which permits the addition of books through the process of continuous revelation. These canons have developed through debate and agreement by the authorities of their respective faiths. Believers consider canonical books as inspired by God or as expressive of the history of the relationship between God and his people. Differences exist between the Jewish Tanakh and Christian biblical canons, and between the canons of different Christian denominations, the differing criteria and processes of canonization dictate what the various communities regard as inspired scripture. In some cases where varying strata of scriptural inspiration have accumulated, Rabbinic Judaism recognizes the twenty-four books of the Masoretic Text, commonly called the Tanakh or Hebrew Bible. According to Marc Zvi Brettler, the Jewish scriptures outside the Torah, the book of Deuteronomy includes a prohibition against adding or subtracting which might apply to the book itself or to the instruction received by Moses on Mt. Sinai. The Book of Nehemiah suggests that the priest-scribe Ezra brought the Torah back from Babylon to Jerusalem, both I and II Maccabees suggest that Judas Maccabeus likewise collected sacred books, indeed some scholars argue that the Jewish canon was fixed by the Hasmonean dynasty. However, these sources do not suggest that the canon was at that time closed, moreover. They lived in a period of two centuries ending c.70 AD. In addition to the Tanakh, mainstream Rabbinic Judaism considers the Talmud to be another central and it takes the form of a record of rabbinic discussions pertaining to Jewish law, ethics, philosophy, customs, and history. There are numerous citations of Sirach within the Talmud, even though the book was not ultimately accepted into the Hebrew canon, the Talmud is the basis for all codes of rabbinic law and is often quoted in other rabbinic literature. Certain groups of Jews, such as the Karaites, do not accept the oral Law as it is codified in the Talmud, Ethiopian Jews—also known as Beta Israel —possess a canon of scripture that is distinct from Rabbinic Judaism. Mäṣḥafä Kedus is the name for the literature of these Jews. Their holiest book, the Orit, consists of the Pentateuch, as well as Joshua, Judges, the rest of the Ethiopian Jewish canon is considered to be of secondary importance. It consists of the remainder of the Hebrew canon—with the possible exception of the Book of Lamentations—and various deuterocanonical books. These include Sirach, Judith, Tobit,1 and 2 Esdras,1 and 4 Baruch, the three books of Meqabyan, Jubilees, Enoch, the Testament of Abraham, the Testament of Isaac, the latter three patriarchal testaments are distinct to this scriptural tradition
15.
New Testament
–
The New Testament is the second major part of the Christian biblical canon, the first part being the Old Testament, based on the Hebrew Bible. The New Testament discusses the teachings and person of Jesus, as well as events in first-century Christianity, Christians regard both the Old and New Testaments together as sacred scripture. The New Testament has frequently accompanied the spread of Christianity around the world and it reflects and serves as a source for Christian theology and morality. Both extended readings and phrases directly from the New Testament are also incorporated into the various Christian liturgies, the New Testament has influenced religious, philosophical, and political movements in Christendom and left an indelible mark on literature, art, and music. In almost all Christian traditions today, the New Testament consists of 27 books, John A. T. Robinson, Dan Wallace, and William F. Albright dated all the books of the New Testament before 70 AD. Others give a date of 80 AD, or at 96 AD. Over time, some disputed books, such as the Book of Revelation, other works earlier held to be Scripture, such as 1 Clement, the Shepherd of Hermas, and the Diatessaron, were excluded from the New Testament. However, the canon of the New Testament, at least since Late Antiquity, has been almost universally recognized within Christianity. The term new testament, or new covenant first occurs in Jeremiah 31,31, the same Greek phrase for new covenant is found elsewhere in the New Testament. Modern English, like Latin, distinguishes testament and covenant as alternative translations, John Wycliffes 1395 version is a translation of the Latin Vulgate and so follows different terms in Jeremiah and Hebrews, Lo. Days shall come, saith the Lord, and I shall make a new covenant with the house of Israel, for he reproving him saith, Lo. Days come, saith the Lord, when I shall establish a new testament on the house of Israel, use of the term New Testament to describe a collection of first and second-century Christian Greek Scriptures can be traced back to Tertullian. In Against Marcion, written circa 208 AD, he writes of the Divine Word, by the 4th century, the existence—even if not the exact contents—of both an Old and New Testament had been established. Lactantius, a 3rd–4th century Christian author wrote in his early-4th-century Latin Institutiones Divinae and that which preceded the advent and passion of Christ—that is, the law and the prophets—is called the Old, but those things which were written after His resurrection are named the New Testament. The canon of the New Testament is the collection of books that most Christians regard as divinely inspired, several of these writings sought to extend, interpret, and apply apostolic teaching to meet the needs of Christians in a given locality. The book order is the same in the Greek Orthodox, Roman Catholic, the Slavonic, Armenian and Ethiopian traditions have different New Testament book orders. Each of the four gospels in the New Testament narrates the life, death, the word gospel derives from the Old English gōd-spell, meaning good news or glad tidings. The gospel was considered the good news of the coming Kingdom of Messiah, and the redemption through the life and death of Jesus, Gospel is a calque of the Greek word εὐαγγέλιον, euangelion
16.
Atomic mass
–
The atomic mass is the mass of an atom. Its unit is the atomic mass units where 1 unified atomic mass unit is defined as 1⁄12 of the mass of a single carbon-12 atom. For atoms, the protons and neutrons of the account for almost all of the mass. When divided by unified atomic mass units or daltons to form a pure numeric ratio, thus, the atomic mass of a carbon-12 atom is 12 u or 12 daltons, but the relative isotopic mass of a carbon-12 atom is simply 12. By contrast, atomic mass figures refer to an individual species, as atoms of the same species are identical. Atomic mass figures are commonly reported to many more significant figures than atomic weights. Standard atomic weight is related to atomic mass by the ranking of isotopes for each element. It is usually about the value as the atomic mass of the most abundant isotope. The atomic mass of atoms, ions, or atomic nuclei is slightly less than the sum of the masses of their constituent protons, neutrons, and electrons, due to binding energy mass loss. Relative isotopic mass is similar to mass and has exactly the same numerical value as atomic mass. The only difference in case, is that relative isotopic mass is a pure number with no units. This loss of results from the use of a scaling ratio with respect to a carbon-12 standard. The relative isotopic mass, then, is the mass of an isotope, when this value is scaled by the mass of carbon-12. Equivalently, the isotopic mass of an isotope or nuclide is the mass of the isotope relative to 1/12 of the mass of a carbon-12 atom. For example, the isotopic mass of a carbon-12 atom is exactly 12. For comparison, the mass of a carbon-12 atom is exactly 12 daltons or 12 unified atomic mass units. Alternately, the mass of a carbon-12 atom may be expressed in any other mass units, for example. As in the case of mass, no nuclides other than carbon-12 have exactly whole-number values of relative isotopic mass
17.
Avogadro constant
–
In chemistry and physics, the Avogadro constant is the number of constituent particles, usually atoms or molecules, that are contained in the amount of substance given by one mole. Thus, it is the proportionality factor that relates the mass of a compound to the mass of a sample. Avogadros constant, often designated with the symbol NA or L, has the value 7023602214085700000♠6. 022140857×1023 mol−1 in the International System of Units and this number is also known as Loschmidt constant in German literature. The constant was later redefined as the number of atoms in 12 grams of the isotope carbon-12, for instance, to a first approximation,1 gram of hydrogen element, having the atomic number 1, has 7023602200000000000♠6. 022×1023 hydrogen atoms. Similarly,12 grams of 12C, with the mass number 12, has the number of carbon atoms. Avogadros number is a quantity, and has the same numerical value of the Avogadro constant given in base units. In contrast, the Avogadro constant has the dimension of reciprocal amount of substance, the Avogadro constant can also be expressed as 0.602214. ML mol−1 Å−3, which can be used to convert from volume per molecule in cubic ångströms to molar volume in millilitres per mole, revisions in the base set of SI units necessitated redefinitions of the concepts of chemical quantity. Avogadros number, and its definition, was deprecated in favor of the Avogadro constant, the French physicist Jean Perrin in 1909 proposed naming the constant in honor of Avogadro. Perrin won the 1926 Nobel Prize in Physics, largely for his work in determining the Avogadro constant by several different methods, accurate determinations of Avogadros number require the measurement of a single quantity on both the atomic and macroscopic scales using the same unit of measurement. This became possible for the first time when American physicist Robert Millikan measured the charge on an electron in 1910, the electric charge per mole of electrons is a constant called the Faraday constant and had been known since 1834 when Michael Faraday published his works on electrolysis. By dividing the charge on a mole of electrons by the charge on a single electron the value of Avogadros number is obtained, since 1910, newer calculations have more accurately determined the values for the Faraday constant and the elementary charge. Perrin originally proposed the name Avogadros number to refer to the number of molecules in one gram-molecule of oxygen, with this recognition, the Avogadro constant was no longer a pure number, but had a unit of measurement, the reciprocal mole. While it is rare to use units of amount of other than the mole, the Avogadro constant can also be expressed in units such as the pound mole. NA = 7026273159734000000♠2. 73159734×1026 −1 = 7025170724843400000♠1. 707248434×1025 −1 Avogadros constant is a factor between macroscopic and microscopic observations of nature. As such, it provides the relationship between other physical constants and properties. The Avogadro constant also enters into the definition of the atomic mass unit. The earliest accurate method to measure the value of the Avogadro constant was based on coulometry
18.
Deuterium
–
Deuterium is one of two stable isotopes of hydrogen. The nucleus of deuterium, called a deuteron, contains one proton and one neutron, whereas the far more common hydrogen isotope, Deuterium has a natural abundance in Earths oceans of about one atom in 6420 of hydrogen. Thus deuterium accounts for approximately 0. 0156% of all the naturally occurring hydrogen in the oceans, the abundance of deuterium changes slightly from one kind of natural water to another. The deuterium isotopes name is formed from the Greek deuteros meaning second, Deuterium was discovered and named in 1931 by Harold Urey. When the neutron was discovered in 1932, this made the structure of deuterium obvious. Soon after deuteriums discovery, Urey and others produced samples of water in which the deuterium content had been highly concentrated. Deuterium is destroyed in the interiors of stars faster than it is produced, other natural processes are thought to produce only an insignificant amount of deuterium. Nearly all deuterium found in nature was produced in the Big Bang 13.8 billion years ago and this is the ratio found in the gas giant planets, such as Jupiter. However, other bodies are found to have different ratios of deuterium to hydrogen-1. This is thought to be as a result of natural isotope separation processes that occur from solar heating of ices in comets, like the water-cycle in Earths weather, such heating processes may enrich deuterium with respect to protium. The analysis of ratios in comets found results very similar to the mean ratio in Earths oceans. This reinforces theories that much of Earths ocean water is of cometary origin, the deuterium/protium ratio of the comet 67P/Churyumov-Gerasimenko, as measured by the Rosetta space probe, is about three times that of earth water. This figure is the highest yet measured in a comet, deuterium/protium ratios thus continue to be an active topic of research in both astronomy and climatology. Deuterium is frequently represented by the chemical symbol D, since it is an isotope of hydrogen with mass number 2, it is also represented by 2H. IUPAC allows both D and 2H, although 2H is preferred, a distinct chemical symbol is used for convenience because of the isotopes common use in various scientific processes. In quantum mechanics the energy levels of electrons in atoms depend on the mass of the system of electron. For hydrogen, this amount is about 1837/1836, or 1.000545, the energies of spectroscopic lines for deuterium and light-hydrogen therefore differ by the ratios of these two numbers, which is 1.000272. The wavelengths of all deuterium spectroscopic lines are shorter than the lines of light hydrogen
19.
Catalysis
–
Catalysis is the increase in the rate of a chemical reaction due to the participation of an additional substance called a catalyst. In most cases, reactions occur faster with a catalyst because they require less activation energy, furthermore, since they are not consumed in the catalyzed reaction, catalysts can continue to act repeatedly. Often only tiny amounts are required in principle, in the presence of a catalyst, less free energy is required to reach the transition state, but the total free energy from reactants to products does not change. A catalyst may participate in multiple chemical transformations, the effect of a catalyst may vary due to the presence of other substances known as inhibitors or poisons or promoters. Catalyzed reactions have an activation energy than the corresponding uncatalyzed reaction, resulting in a higher reaction rate at the same temperature. However, the mechanics of catalysis is complex. Usually, the catalyst participates in this slowest step, and rates are limited by amount of catalyst, in heterogeneous catalysis, the diffusion of reagents to the surface and diffusion of products from the surface can be rate determining. A nanomaterial-based catalyst is an example of a heterogeneous catalyst, analogous events associated with substrate binding and product dissociation apply to homogeneous catalysts. Although catalysts are not consumed by the reaction itself, they may be inhibited, deactivated, in heterogeneous catalysis, typical secondary processes include coking where the catalyst becomes covered by polymeric side products. Additionally, heterogeneous catalysts can dissolve into the solution in a system or sublimate in a solid–gas system. The production of most industrially important chemicals involves catalysis, similarly, most biochemically significant processes are catalysed. Research into catalysis is a field in applied science and involves many areas of chemistry, notably organometallic chemistry. Catalysis is relevant to aspects of environmental science, e. g. the catalytic converter in automobiles. Many transition metals and transition metal complexes are used in catalysis as well, Catalysts called enzymes are important in biology. A catalyst works by providing a reaction pathway to the reaction product. The rate of the reaction is increased as this route has a lower activation energy than the reaction route not mediated by the catalyst. The disproportionation of hydrogen peroxide creates water and oxygen, as shown below,2 H2O2 →2 H2O + O2 This reaction is preferable in the sense that the reaction products are more stable than the starting material, though the uncatalysed reaction is slow. In fact, the decomposition of hydrogen peroxide is so slow that hydrogen peroxide solutions are commercially available and this reaction is strongly affected by catalysts such as manganese dioxide, or the enzyme peroxidase in organisms
20.
Density
–
The density, or more precisely, the volumetric mass density, of a substance is its mass per unit volume. The symbol most often used for density is ρ, although the Latin letter D can also be used. Mathematically, density is defined as mass divided by volume, ρ = m V, where ρ is the density, m is the mass, and V is the volume. In some cases, density is defined as its weight per unit volume. For a pure substance the density has the numerical value as its mass concentration. Different materials usually have different densities, and density may be relevant to buoyancy, purity, osmium and iridium are the densest known elements at standard conditions for temperature and pressure but certain chemical compounds may be denser. Thus a relative density less than one means that the floats in water. The density of a material varies with temperature and pressure and this variation is typically small for solids and liquids but much greater for gases. Increasing the pressure on an object decreases the volume of the object, increasing the temperature of a substance decreases its density by increasing its volume. In most materials, heating the bottom of a results in convection of the heat from the bottom to the top. This causes it to rise relative to more dense unheated material, the reciprocal of the density of a substance is occasionally called its specific volume, a term sometimes used in thermodynamics. Density is a property in that increasing the amount of a substance does not increase its density. Archimedes knew that the irregularly shaped wreath could be crushed into a cube whose volume could be calculated easily and compared with the mass, upon this discovery, he leapt from his bath and ran naked through the streets shouting, Eureka. As a result, the term eureka entered common parlance and is used today to indicate a moment of enlightenment, the story first appeared in written form in Vitruvius books of architecture, two centuries after it supposedly took place. Some scholars have doubted the accuracy of this tale, saying among other things that the method would have required precise measurements that would have been difficult to make at the time, from the equation for density, mass density has units of mass divided by volume. As there are units of mass and volume covering many different magnitudes there are a large number of units for mass density in use. The SI unit of kilogram per metre and the cgs unit of gram per cubic centimetre are probably the most commonly used units for density.1,000 kg/m3 equals 1 g/cm3. In industry, other larger or smaller units of mass and or volume are often more practical, see below for a list of some of the most common units of density
21.
Amount of substance
–
Amount of substance is a standards-defined quantity that measures the size of an ensemble of elementary entities, such as atoms, molecules, electrons, and other particles. It is sometimes referred to as chemical amount, the International System of Units defines the amount of substance to be proportional to the number of elementary entities present. The SI unit for amount of substance is the mole and it has the unit symbol mol. The proportionality constant is the inverse of the Avogadro constant, the mole is defined as the amount of substance that contains an equal number of elementary entities as there are atoms in 12g of the isotope carbon-12. This number is called Avogadros number and has the value 6. 022140857×1023 and it is the numerical value of the Avogadro constant which has the unit 1/mol, and relates the molar mass of an amount of substance to its mass. Therefore, the amount of substance of a sample is calculated as the sample mass divided by the mass of the substance. Amount of substance appears in thermodynamic relations such as the gas law. Another unit of amount of substance in use in engineering in the United States is the pound-mole. When quoting an amount of substance, it is necessary to specify the entity involved, unless there is no risk of ambiguity. One mole of chlorine could refer either to chlorine atoms, as in 58.44 g of sodium chloride, or to chlorine molecules, the simplest way to avoid ambiguity is to replace the term substance by the name of the entity or to quote the empirical formula. The main derived quantity in which amount of substance enters into the numerator is amount of substance concentration and this name is often abbreviated to amount concentration, except in clinical chemistry where substance concentration is the preferred term to avoid ambiguity with mass concentration. The term molar concentration is incorrect, but commonly used, the alchemists, and especially the early metallurgists, probably had some notion of amount of substance, but there are no surviving records of any generalization of the idea beyond a set of recipes. In 1758, Mikhail Lomonosov questioned the idea that mass was the measure of the quantity of matter. The development of the concept of amount of substance was coincidental with, and vital to,1777, Wenzel publishes Lessons on Affinity, in which he demonstrates that the proportions of the base component and the acid component remain the same during reactions between two neutral salts. 1789, Lavoisier publishes Treatise of Elementary Chemistry, introducing the concept of a chemical element,1792, Richter publishes the first volume of Stoichiometry or the Art of Measuring the Chemical Elements. The term stoichiometry is used for the first time, the first tables of equivalent weights are published for acid–base reactions. Richter also notes that, for an acid, the equivalent mass of the acid is proportional to the mass of oxygen in the base. 1794, Prousts Law of definite proportions generalizes the concept of equivalent weights to all types of chemical reaction,1805, Dalton publishes his first paper on modern atomic theory, including a Table of the relative weights of the ultimate particles of gaseous and other bodies
22.
Diatomic molecule
–
Diatomic molecules are molecules composed of only two atoms, of the same or different chemical elements. The prefix di- is of Greek origin, meaning two, if a diatomic molecule consists of two atoms of the same element, such as hydrogen or oxygen, then it is said to be homonuclear. Otherwise, if a molecule consists of two different atoms, such as carbon monoxide or nitric oxide, the molecule is said to be heteronuclear. The only chemical elements that form stable homonuclear diatomic molecules at temperature and pressure are the gases hydrogen, nitrogen, oxygen, fluorine. The noble gases are gases at STP, but they are monatomic. The homonuclear diatomic gases and noble gases together are called elemental gases or molecular gases, at slightly elevated temperatures, the halogens bromine and iodine also form diatomic gases. All halogens have been observed as diatomic molecules, except for astatine, other elements form diatomic molecules when evaporated, but these diatomic species repolymerize when cooled. Heating elemental phosphorus gives diphosphorus, P2, dilithium is known in the gas phase. Ditungsten and dimolybdenum form with sextuple bonds in the gas phase, the bond in a homonuclear diatomic molecule is non-polar. All other diatomic molecules are chemical compounds of two different elements, many elements can combine to form heteronuclear diatomic molecules, depending on temperature and pressure. Common examples include the carbon monoxide, nitric oxide. Hundreds of diatomic molecules have been identified in the environment of the Earth, in the laboratory, about 99% of the Earths atmosphere is composed of two species of diatomic molecules, nitrogen and oxygen. The natural abundance of hydrogen in the Earths atmosphere is only of the order of parts per million, the interstellar medium is, indeed, dominated by hydrogen atoms. John Daltons original atomic hypothesis assumed that all elements were monatomic, for example, Dalton assumed waters formula to be HO, giving the atomic weight of oxygen as eight times that of hydrogen, instead of the modern value of about 16. As a consequence, confusion existed regarding atomic weights and molecular formulas for about half a century, at the 1860 Karlsruhe Congress on atomic weights, Cannizzaro resurrected Avogadros ideas and used them to produce a consistent table of atomic weights, which mostly agree with modern values. These weights were an important prerequisite for the discovery of the law by Dmitri Mendeleev. Diatomic molecules are normally in their lowest or ground state, which conventionally is also known as the X state, such excitation can also occur when the gas absorbs light or other electromagnetic radiation. The excited states are unstable and naturally relax back to the ground state, over various short time scales after the excitation, transitions occur from higher to lower electronic states and ultimately to the ground state, and in each transition results a photon is emitted
23.
Hydrogen
–
Hydrogen is a chemical element with chemical symbol H and atomic number 1. With a standard weight of circa 1.008, hydrogen is the lightest element on the periodic table. Its monatomic form is the most abundant chemical substance in the Universe, non-remnant stars are mainly composed of hydrogen in the plasma state. The most common isotope of hydrogen, termed protium, has one proton, the universal emergence of atomic hydrogen first occurred during the recombination epoch. At standard temperature and pressure, hydrogen is a colorless, odorless, tasteless, non-toxic, nonmetallic, since hydrogen readily forms covalent compounds with most nonmetallic elements, most of the hydrogen on Earth exists in molecular forms such as water or organic compounds. Hydrogen plays an important role in acid–base reactions because most acid-base reactions involve the exchange of protons between soluble molecules. In ionic compounds, hydrogen can take the form of a charge when it is known as a hydride. The hydrogen cation is written as though composed of a bare proton, Hydrogen gas was first artificially produced in the early 16th century by the reaction of acids on metals. Industrial production is mainly from steam reforming natural gas, and less often from more energy-intensive methods such as the electrolysis of water. Most hydrogen is used near the site of its production, the two largest uses being fossil fuel processing and ammonia production, mostly for the fertilizer market, Hydrogen is a concern in metallurgy as it can embrittle many metals, complicating the design of pipelines and storage tanks. Hydrogen gas is flammable and will burn in air at a very wide range of concentrations between 4% and 75% by volume. The enthalpy of combustion is −286 kJ/mol,2 H2 + O2 →2 H2O +572 kJ Hydrogen gas forms explosive mixtures with air in concentrations from 4–74%, the explosive reactions may be triggered by spark, heat, or sunlight. The hydrogen autoignition temperature, the temperature of spontaneous ignition in air, is 500 °C, the detection of a burning hydrogen leak may require a flame detector, such leaks can be very dangerous. Hydrogen flames in other conditions are blue, resembling blue natural gas flames, the destruction of the Hindenburg airship was a notorious example of hydrogen combustion and the cause is still debated. The visible orange flames in that incident were the result of a mixture of hydrogen to oxygen combined with carbon compounds from the airship skin. H2 reacts with every oxidizing element, the ground state energy level of the electron in a hydrogen atom is −13.6 eV, which is equivalent to an ultraviolet photon of roughly 91 nm wavelength. The energy levels of hydrogen can be calculated fairly accurately using the Bohr model of the atom, however, the atomic electron and proton are held together by electromagnetic force, while planets and celestial objects are held by gravity. The most complicated treatments allow for the effects of special relativity
24.
Exothermic reaction
–
An exothermic reaction is a chemical reaction that releases energy by light or heat. It is the opposite of an endothermic reaction, expressed in a chemical equation, reactants → products + energy An exothermic reaction is a chemical or physical reaction that releases heat. It gives net energy to its surroundings and that is, the energy needed to initiate the reaction is less than the energy released. When the medium in which the reaction is taking place gains heat, when using a calorimeter, the total amount of heat that flows into the calorimeter is the negative of the net change in energy of the system. The absolute amount of energy in a system is difficult to measure or calculate. The enthalpy change, ΔH, of a reaction is much easier to work with. The enthalpy change equals the change in energy of the system plus the work needed to change the volume of the system against constant ambient pressure. A bomb calorimeter is very suitable for measuring the change, ΔH. In endergonic reactions and exergonic reactions it is the sign of the Gibbs free energy that determines the equilibrium point, the related concepts endergonic and exergonic apply to all physical processes. The conceptually related endotherm and ectotherm are concepts in animal physiology, in quantum numbers, when any excited energy level goes down to its original level for example, when n=4 fall to n=2, energy is released so, it is exothermic. Where an exothermic reaction causes heating of the vessel which is not controlled. This positive feedback situation is known as thermal runaway, an explosion can also result from the problem. Heat production or absorption in either a process or chemical reaction is measured using calorimetry. One common laboratory instrument is the calorimeter, where the heat flow into or from the reaction vessel is monitored. The technique can be used to follow chemical reactions as well as physical processes such as crystallization and dissolution, energy released is measured in Joule per mole. The reaction has a negative ΔH value due to heat loss, E. g. -123 J/mol Chemical thermodynamics Differential scanning calorimetry Endergonic Exergonic Endergonic reaction Exergonic reaction Exothermic Endothermic reaction Endotherm
25.
Mole (unit)
–
The mole is the unit of measurement in the International System of Units for amount of substance. This number is expressed by the Avogadro constant, which has a value of 6. 022140857×1023 mol−1, the mole is one of the base units of the SI, and has the unit symbol mol. The mole is used in chemistry as a convenient way to express amounts of reactants and products of chemical reactions. For example, the chemical equation 2 H2 + O2 →2 H2O implies that 2 moles of dihydrogen and 1 mole of dioxygen react to form 2 moles of water. The mole may also be used to express the number of atoms, ions, the concentration of a solution is commonly expressed by its molarity, defined as the number of moles of the dissolved substance per litre of solution. For example, the relative molecular mass of natural water is about 18.015, therefore. The term gram-molecule was formerly used for essentially the same concept, the term gram-atom has been used for a related but distinct concept, namely a quantity of a substance that contains Avogadros number of atoms, whether isolated or combined in molecules. Thus, for example,1 mole of MgBr2 is 1 gram-molecule of MgBr2 but 3 gram-atoms of MgBr2, in honor of the unit, some chemists celebrate October 23, which is a reference to the 1023 scale of the Avogadro constant, as Mole Day. Some also do the same for February 6 and June 2, thus, by definition, one mole of pure 12C has a mass of exactly 12 g. It also follows from the definition that X moles of any substance will contain the number of molecules as X moles of any other substance. The mass per mole of a substance is called its molar mass, the number of elementary entities in a sample of a substance is technically called its amount. Therefore, the mole is a convenient unit for that physical quantity, one can determine the chemical amount of a known substance, in moles, by dividing the samples mass by the substances molar mass. Other methods include the use of the volume or the measurement of electric charge. The mass of one mole of a substance depends not only on its molecular formula, since the definition of the gram is not mathematically tied to that of the atomic mass unit, the number NA of molecules in a mole must be determined experimentally. The value adopted by CODATA in 2010 is NA =6. 02214129×1023 ±0. 00000027×1023, in 2011 the measurement was refined to 6. 02214078×1023 ±0. 00000018×1023. The number of moles of a sample is the sample mass divided by the mass of the material. The history of the mole is intertwined with that of mass, atomic mass unit, Avogadros number. The first table of atomic mass was published by John Dalton in 1805
26.
Copper
–
Copper is a chemical element with symbol Cu and atomic number 29. It is a soft, malleable, and ductile metal with high thermal and electrical conductivity. A freshly exposed surface of copper has a reddish-orange color. Copper is one of the few metals that occur in nature in directly usable metallic form as opposed to needing extraction from an ore and this led to very early human use, from c.8000 BC. Copper used in buildings, usually for roofing, oxidizes to form a green verdigris, Copper is sometimes used in decorative art, both in its elemental metal form and in compounds as pigments. Copper compounds are used as agents, fungicides, and wood preservatives. Copper is essential to all living organisms as a trace dietary mineral because it is a key constituent of the enzyme complex cytochrome c oxidase. In molluscs and crustaceans, copper is a constituent of the blood pigment hemocyanin, replaced by the hemoglobin in fish. In humans, copper is found mainly in the liver, muscle, the adult body contains between 1.4 and 2.1 mg of copper per kilogram of body weight. The filled d-shells in these elements contribute little to interatomic interactions, unlike metals with incomplete d-shells, metallic bonds in copper are lacking a covalent character and are relatively weak. This observation explains the low hardness and high ductility of single crystals of copper, at the macroscopic scale, introduction of extended defects to the crystal lattice, such as grain boundaries, hinders flow of the material under applied stress, thereby increasing its hardness. For this reason, copper is supplied in a fine-grained polycrystalline form. The softness of copper partly explains its high conductivity and high thermal conductivity. The maximum permissible current density of copper in open air is approximately 3. 1×106 A/m2 of cross-sectional area, Copper is one of a few metallic elements with a natural color other than gray or silver. Pure copper is orange-red and acquires a reddish tarnish when exposed to air, as with other metals, if copper is put in contact with another metal, galvanic corrosion will occur. A green layer of verdigris can often be seen on old structures, such as the roofing of many older buildings. Copper tarnishes when exposed to sulfur compounds, with which it reacts to form various copper sulfides. There are 29 isotopes of copper, 63Cu and 65Cu are stable, with 63Cu comprising approximately 69% of naturally occurring copper, both have a spin of 3⁄2
27.
Silver nitrate
–
Silver nitrate is an inorganic compound with chemical formula AgNO3. This compound is a precursor to many other silver compounds. It is far less sensitive to light than the halides and it was once called lunar caustic because silver was called luna by the ancient alchemists, who believed that silver was associated with the moon. In solid silver nitrate, the ions are three-coordinated in a trigonal planar arrangement. Albertus Magnus, in the 13th century, documented the ability of nitric acid to separate gold, Magnus noted that the resulting solution of silver nitrate could blacken skin. Silver nitrate can be prepared by reacting silver, such as a silver bullion or silver foil, with acid, resulting in silver nitrate, water. Reaction byproducts depend upon the concentration of acid used. 3 Ag +4 HNO3 →3 AgNO3 +2 H2O + NO Ag +2 HNO3 → AgNO3 + H2O + NO2 This is performed under a fume hood because of nitrogen oxide evolved during the reaction. A typical reaction with silver nitrate is to suspend a rod of copper in a solution of silver nitrate, silver nitrate is the least expensive salt of silver, it offers several other advantages as well. It is non-hygroscopic, in contrast to silver fluoroborate and silver perchlorate and it is relatively stable to light. Finally, it dissolves in solvents, including water. The nitrate can be replaced by other ligands, rendering AgNO3 versatile. Treatment with solutions of halide ions gives a precipitate of AgX, similarly, silver nitrate is used to prepare some silver-based explosives, such as the fulminate, azide, or acetylide, through a precipitation reaction. This reaction is used in inorganic chemistry to abstract halides, Ag+ + X− → AgX where X− = Cl−, Br−. Other silver salts with non-coordinating anions, namely silver tetrafluoroborate and silver hexafluorophosphate are used for demanding applications. Similarly, this reaction is used in chemistry to confirm the presence of chloride, bromide. Samples are typically acidified with nitric acid to remove interfering ions, e. g. carbonate ions. This step avoids confusion of silver sulfide or silver carbonate precipitates with that of silver halides, the color of precipitate varies with the halide, white, pale yellow/cream, yellow
28.
Silver
–
Silver is a metallic element with symbol Ag and atomic number 47. The symbol Ag stems from Latin argentum, derived from the Greek ὰργὀς, a soft, white, lustrous transition metal, it exhibits the highest electrical conductivity, thermal conductivity, and reflectivity of any metal. The metal is found in the Earths crust in the pure, free form, as an alloy with gold and other metals. Most silver is produced as a byproduct of copper, gold, lead, Silver is more abundant than gold, but it is much less abundant as a native metal. Its purity is measured on a per mille basis, a 94%-pure alloy is described as 0.940 fine. As one of the seven metals of antiquity, silver has had a role in most human cultures. Silver has long valued as a precious metal. Silver metal is used in many premodern monetary systems in bullion coins, Silver is used in numerous applications other than currency, such as solar panels, water filtration, jewelry, ornaments, high-value tableware and utensils, and as an investment medium. Silver is used industrially in electrical contacts and conductors, in specialized mirrors, window coatings, Silver compounds are used in photographic film and X-rays. Dilute silver nitrate solutions and other compounds are used as disinfectants and microbiocides, added to bandages and wound-dressings, catheters. Silver is similar in its physical and chemical properties to its two neighbours in group 11 of the periodic table, copper and gold. This distinctive electron configuration, with an electron in the highest occupied s subshell over a filled d subshell. Silver is a soft, ductile and malleable transition metal. Silver crystallizes in a cubic lattice with bulk coordination number 12. Unlike metals with incomplete d-shells, metallic bonds in silver are lacking a covalent character and are relatively weak and this observation explains the low hardness and high ductility of single crystals of silver. Silver has a brilliant white metallic luster that can take a polish. Protected silver has greater optical reflectivity than aluminium at all wavelengths longer than ~450 nm, at wavelengths shorter than 450 nm, silvers reflectivity is inferior to that of aluminium and drops to zero near 310 nm. The electrical conductivity of silver is the greatest of all metals, greater even than copper, during World War II in the US,13540 tons of silver were used in electromagnets for enriching uranium, mainly because of the wartime shortage of copper
29.
Single displacement reaction
–
A single-displacement reaction is a reaction by which an element replaces another element in a compound. It can be represented generically as, A + B-C → A-C + B This will most often occur if A is more reactive than B, thus giving a more stable product. A and B must be either, Different metals, in which case C represents an anion, or Halogens, in either case, when AC and BC are aqueous compounds, C is a spectator ion. In the activity or reactivity series, the metals with the highest propensity to donate their electrons to react are listed first, therefore, a metal higher on the list is able to displace anything on the list below it. The order of activity for metals, from most reactive to least reactive, is Li, K, Sr, Na, Ca, Mg, Al, Zn, Cr, Fe, Cd, Co, Ni, Sn, Pb, H, Sb, As, Bi, Cu, Hg, Ag, Pd, Pt, Au. Similarly, the halogens with the highest propensity to acquire electrons are the most reactive, the activity series for halogens, from highest to lowest, is F, Cl, Br, I. Due to the state nature of A and B, all single displacement reactions are also oxidation-reduction reactions. When A and B are metals, A is always oxidized, since halogens prefer to gain electrons, A is reduced and B is oxidized when A and B represent those elements. A and B may have different charge as ions and therefore some balancing of the equation may be necessary, for example, the reaction between silver nitrate, AgNO3, and zinc, Zn, forms silver, Ag, and zinc nitrate, Zn2. 2AgNO3 + Zn → 2Ag + Zn 2 All simple metal with acid reactions are single displacement reactions, for example, the reaction between magnesium, Mg, and hydrochloric acid, HCl, forms magnesium chloride, MgCl2, and hydrogen, H2. Mg +2 HCl → MgCl 2 + H2 One cation replaces another, a cation is a positively charged ion or a metal. When it is written in generic symbols, it is written out like this, X + YZ → XZ + Y Element X has replaced Y in compound YZ to become a new compound XZ and the free element Y. This is an oxidation–reduction reaction wherein element Y is reduced from a cation into the elemental form, some examples of this would be the reverse reactions to these, Ag + Cu2 → No reaction Au + HCl → No reaction One anion replaces another. An anion is a charged ion or a nonmetal. Written using generic symbol, it is, A + XY → XA + Y Element A has replaced Y to form a new compound XA and the free element Y. This is an oxidation-reduction reaction wherein element A is reduced from the form into an anion
30.
Copper(II) nitrate
–
Copper nitrate, Cu2, is an inorganic compound that forms a blue crystalline solid. Anhydrous copper nitrate forms deep blue-green crystals and sublimes in a vacuum at 150-200 °C, Copper nitrate also occurs as five different hydrates, the most common ones being the trihydrate and hexahydrate. These materials are commonly encountered in commerce than in the laboratory. At 80 °C, the convert to basic copper nitrate. Exploiting this reactivity, copper nitrate can be used to generate nitric acid by heating it until decomposition and this method is similar to the last step in the Ostwald process. Anhydrous copper nitrate has been crystallized in two solvate-free polymorphs, α- and β-Cu2 are fully 3D coordination polymer networks. The alpha form has only one Cu environment, with coordination, the nitromethane solvate also features coordination, with four short Cu-O bonds of approximately 200 pm and one longer bond at 240 pm. They are coordination polymers, with chains of copper centers. In the gas phase, copper nitrate features two bidentate nitrate ligands, thus, evaporation of the solid entails cracking to give the copper nitrate molecule. Five hydrates have been reported, the monohydrate, the sesquihydrate, the hemipentahydrate, a trihydrate, the hexahydrate is interesting because the Cu-O distances are all equal, not revealing the usual effect of Jahn-Teller distortion that is otherwise characteristic of octahedral Cu complexes. This non-effect is attributed to the hydrogen bonding that limits the elasticity of the Cu-O bonds. Copper nitrate finds a variety of applications, the one being its conversion to copper oxide. Its solutions are used in textiles and polishing agents for other metals, Copper nitrates are found in some pyrotechnics. It is often used in laboratories to demonstrate chemical voltaic cell reactions. Hydrated copper nitrate adsorbed onto clay affords a reagent called Claycop, the resulting blue-colored clay is used as a slurry, for example for the oxidation of thiols to disulfides. Claycop is also used to convert dithioacetals to carbonyls, a related reagent based on montmorillonite has proven useful for the nitration of aromatic compounds. National Pollutant Inventory – Copper and compounds fact sheet ICSC Copper and compounds fact sheet
31.
Propane
–
Propane is a three-carbon alkane with the molecular formula C3H8, a gas, at standard temperature and pressure, but compressible to a transportable liquid. A by-product of natural gas processing and petroleum refining, it is used as a fuel for engines, oxy-gas torches, portable stoves. Propane is one of a group of liquefied petroleum gases, the others include butane, propylene, butadiene, butylene, isobutylene, and mixtures thereof. Propane was first identified as a component in gasoline by Walter O. Snelling of the U. S. Bureau of Mines in 1910. The volatility of these lighter hydrocarbons caused them to be known as wild because of the vapor pressures of unrefined gasoline. On March 31, the New York Times reported on Snellings work with liquefied gas and that a steel bottle will carry enough gas to light an ordinary home for three weeks. It was during this time that Snelling, in cooperation with Frank P. Peterson, Chester Kerr, together, they established American Gasol Co. the first commercial marketer of propane. Snelling had produced relatively pure propane by 1911, and on March 25,1913, a separate method of producing LP gas through compression was created by Frank Peterson and its patent granted on July 2,1912. The 1920s saw increased production of LP gas, with the first year of recorded production totaling 223,000 US gallons in 1922. In 1927, annual marketed LP gas production reached 1 million US gallons, and by 1935, major industry developments in the 1930s included the introduction of railroad tank car transport, gas odorization, and the construction of local bottle-filling plants. The year 1945 marked the first year that annual LP gas sales reached a billion gallons, by 1947, 62% of all U. S. homes had been equipped with either natural gas or propane for cooking. In 1950,1,000 propane-fueled buses were ordered by the Chicago Transit Authority, in 2004 it was reported to be a growing $8-billion to $10-billion industry with over 15 billion US gallons of propane being used annually in the U. S. The prop- root found in propane and names of compounds with three-carbon chains was derived from propionic acid. Propane is produced as a by-product of two processes, natural gas processing and petroleum refining. The processing of natural gas involves removal of butane, propane, additionally, oil refineries produce some propane as a by-product of cracking petroleum into gasoline or heating oil. The supply of propane cannot easily be adjusted to meet increased demand, about 90% of U. S. propane is domestically produced. The United States imports about 10% of the propane consumed each year, with about 70% of that coming from Canada via pipeline, the remaining 30% of imported propane comes to the United States from other sources via ocean transport. After it is produced, North American propane is stored in salt caverns
32.
Thermite reaction
–
Thermite is a pyrotechnic composition of metal powder, fuel and metal oxide. When ignited by heat, thermite undergoes an exothermic reduction-oxidation reaction, most varieties are not explosive but can create brief bursts of high temperature in a small area. Its form of action is similar to that of other fuel-oxidizer mixtures, fuels include aluminium, magnesium, titanium, zinc, silicon, and boron. Aluminium is common because of its boiling point and low cost. Oxidizers include bismuth oxide, boron oxide, silicon oxide, chromium oxide, manganese oxide, iron oxide, iron oxide, copper oxide, the reaction, also called the Goldschmidt process, is used for thermite welding, often used to join rail tracks. Thermites have also used in metal refining, demolition of munitions. Some thermite-like mixtures are used as pyrotechnic initiators in fireworks, the reactants are commonly powdered and mixed with a binder to keep the material solid and prevent separation. Other metal oxides can be used, such as chromium oxide, the thermite reaction was discovered in 1893 and patented in 1895 by German chemist Hans Goldschmidt. Consequently, the reaction is called the Goldschmidt reaction or Goldschmidt process. Goldschmidt was originally interested in producing very pure metals by avoiding the use of carbon in smelting, the first commercial application of thermite was the welding of tram tracks in Essen in 1899. Red iron oxide is the most common iron oxide used in thermite, other oxides are occasionally used, such as MnO2 in manganese thermite, Cr2O3 in chromium thermite, quartz in silicon thermite, or copper oxide in copper thermite, but only for specialized purposes. All of these examples use aluminium as the reactive metal, fluoropolymers can be used in special formulations, Teflon with magnesium or aluminium being a relatively common example. Magnesium/teflon/viton is another pyrolant of this type, combinations of dry ice and reducing agents such as magnesium, aluminum and boron follow the same chemical reaction as with traditional thermite mixtures, producing metal oxides and carbon. Despite the very cold temperature of a dry ice thermite mixture, in principle, any reactive metal could be used instead of aluminium. This is rarely done, because the properties of aluminium are nearly ideal for this reaction, It is by far the cheapest of the highly reactive metals. For example, in Dec 2014, tin was 19,830 USD/Metric Ton, zinc was 2,180 USD/MT and aluminium was 1,910 USD/MT It forms a passivation layer making it safer to handle than many other reactive metals. Its relatively low melting point means that it is easy to melt the metal, so that the reaction can occur mainly in the liquid phase and thus proceeds fairly quickly. Its high boiling point enables the reaction to reach high temperatures
33.
Iron(III) oxide
–
Iron oxide or ferric oxide is the inorganic compound with the formula Fe2O3. It is one of the three main oxides of iron, the two being iron oxide, which is rare, and iron oxide, which also occurs naturally as the mineral magnetite. As the mineral known as hematite, Fe2O3 is the source of iron for the steel industry. Fe2O3 is ferromagnetic, dark red, and readily attacked by acids, Iron oxide is often called rust, and to some extent this label is useful, because rust shares several properties and has a similar composition. To a chemist, rust is considered a material, described as hydrated ferric oxide. Fe2O3 can be obtained in various polymorphs, in the main ones, α and γ, iron adopts octahedral coordination geometry. That is, each Fe center is bound to six oxygen ligands, α-Fe2O3 has the rhombohedral, corundum structure and is the most common form. It occurs naturally as the mineral hematite which is mined as the ore of iron. It is antiferromagnetic below ~260 K, and exhibits weak ferromagnetism between 260 K and the Néel temperature,950 K and it is easy to prepare using both thermal decomposition and precipitation in the liquid phase. Its magnetic properties are dependent on many factors, e. g. pressure, particle size and it is metastable and converted from the alpha phase at high temperatures. It occurs naturally as the mineral maghemite and it is ferromagnetic and finds application in recording tapes, although ultrafine particles smaller than 10 nanometers are superparamagnetic. It can be prepared by thermal dehydratation of gamma iron oxide-hydroxide, another method involves the careful oxidation of Fe3O4. The ultrafine particles can be prepared by decomposition of iron oxalate. Several other phases have been identified or claimed, the β-phase is cubic body centered, metastable, and at temperatures above 500 °C converts to alpha phase. It can be prepared by reduction of hematite by carbon, pyrolysis of iron chloride solution, the epsilon phase is rhombic, and shows properties intermediate between alpha and gamma, and may have useful magnetic properties. Preparation of the pure epsilon phase has proven challenging due to contamination with alpha. Material with a proportion of epsilon phase can be prepared by thermal transformation of the gamma phase. This phase is metastable, transforming to the alpha phase at between 500 and 750 °C
34.
Aluminium
–
Aluminium or aluminum is a chemical element in the boron group with symbol Al and atomic number 13. It is a silvery-white, soft, nonmagnetic, ductile metal, Aluminium metal is so chemically reactive that native specimens are rare and limited to extreme reducing environments. Instead, it is combined in over 270 different minerals. The chief ore of aluminium is bauxite, Aluminium is remarkable for the metals low density and its ability to resist corrosion through the phenomenon of passivation. Aluminium and its alloys are vital to the industry and important in transportation and structures, such as building facades. The oxides and sulfates are the most useful compounds of aluminium, despite its prevalence in the environment, no known form of life uses aluminium salts metabolically, but aluminium is well tolerated by plants and animals. Because of these salts abundance, the potential for a role for them is of continuing interest. Aluminium is a soft, durable, lightweight, ductile. It is nonmagnetic and does not easily ignite, a fresh film of aluminium serves as a good reflector of visible light and an excellent reflector of medium and far infrared radiation. The yield strength of aluminium is 7–11 MPa, while aluminium alloys have yield strengths ranging from 200 MPa to 600 MPa. Aluminium has about one-third the density and stiffness of steel and it is easily machined, cast, drawn and extruded. Aluminium atoms are arranged in a cubic structure. Aluminium has an energy of approximately 200 mJ/m2. Aluminium is a thermal and electrical conductor, having 59% the conductivity of copper. Aluminium is capable of superconductivity, with a critical temperature of 1.2 kelvin. Aluminium is the most common material for the fabrication of superconducting qubits, the strongest aluminium alloys are less corrosion resistant due to galvanic reactions with alloyed copper. This corrosion resistance is reduced by aqueous salts, particularly in the presence of dissimilar metals. In highly acidic solutions, aluminium reacts with water to form hydrogen, primarily because it is corroded by dissolved chlorides, such as common sodium chloride, household plumbing is never made from aluminium
35.
Aluminium oxide
–
Aluminium oxide or aluminum oxide is a chemical compound of aluminium and oxygen with the chemical formula Al2O3. It is the most commonly occurring of several aluminium oxides, and it is commonly called alumina, and may also be called aloxide, aloxite, or alundum depending on particular forms or applications. It occurs naturally in its crystalline polymorphic phase α-Al2O3 as the mineral corundum, varieties of form the precious gemstones ruby. Al2O3 is significant in its use to produce metal, as an abrasive owing to its hardness. Corundum is the most common naturally occurring form of aluminium oxide. Rubies and sapphires are gem-quality forms of corundum, which owe their characteristic colors to trace impurities, rubies are given their characteristic deep red color and their laser qualities by traces of chromium. Sapphires come in different colors given by various other impurities, such as iron, Al2O3 is an electrical insulator but has a relatively high thermal conductivity for a ceramic material. Aluminium oxide is insoluble in water, in its most commonly occurring crystalline form, called corundum or α-aluminium oxide, its hardness makes it suitable for use as an abrasive and as a component in cutting tools. Aluminium oxide is responsible for the resistance of aluminium to weathering. Metallic aluminium is very reactive with oxygen, and a thin passivation layer of aluminium oxide forms on any exposed aluminium surface. This layer protects the metal from further oxidation, the thickness and properties of this oxide layer can be enhanced using a process called anodising. A number of alloys, such as bronzes, exploit this property by including a proportion of aluminium in the alloy to enhance corrosion resistance. Aluminium oxide was taken off the United States Environmental Protection Agencys chemicals lists in 1988, aluminium oxide is on EPAs Toxics Release Inventory list if it is a fibrous form. Al2O3 +6 HF →2 AlF3 +3 H2O Al2O3 +2 NaOH +3 H2O →2 NaAl4 The most common form of aluminium oxide is known as corundum. The oxygen ions form a hexagonal close-packed structure with aluminium ions filling two-thirds of the octahedral interstices. In terms of its crystallography, corundum adopts a trigonal Bravais lattice with a group of R-3c. The primitive cell contains two units of aluminium oxide. Each has a crystal structure and properties
36.
Iron
–
Iron is a chemical element with symbol Fe and atomic number 26. It is a metal in the first transition series and it is by mass the most common element on Earth, forming much of Earths outer and inner core. It is the fourth most common element in the Earths crust, like the other group 8 elements, ruthenium and osmium, iron exists in a wide range of oxidation states, −2 to +6, although +2 and +3 are the most common. Elemental iron occurs in meteoroids and other low oxygen environments, but is reactive to oxygen, fresh iron surfaces appear lustrous silvery-gray, but oxidize in normal air to give hydrated iron oxides, commonly known as rust. Unlike the metals that form passivating oxide layers, iron oxides occupy more volume than the metal and thus flake off, Iron metal has been used since ancient times, although copper alloys, which have lower melting temperatures, were used even earlier in human history. Pure iron is soft, but is unobtainable by smelting because it is significantly hardened and strengthened by impurities, in particular carbon. A certain proportion of carbon steel, which may be up to 1000 times harder than pure iron. Crude iron metal is produced in blast furnaces, where ore is reduced by coke to pig iron, further refinement with oxygen reduces the carbon content to the correct proportion to make steel. Steels and iron alloys formed with metals are by far the most common industrial metals because they have a great range of desirable properties. Iron chemical compounds have many uses, Iron oxide mixed with aluminium powder can be ignited to create a thermite reaction, used in welding and purifying ores. Iron forms binary compounds with the halogens and the chalcogens, among its organometallic compounds is ferrocene, the first sandwich compound discovered. Iron plays an important role in biology, forming complexes with oxygen in hemoglobin and myoglobin. Iron is also the metal at the site of many important redox enzymes dealing with cellular respiration and oxidation and reduction in plants. A human male of average height has about 4 grams of iron in his body and this iron is distributed throughout the body in hemoglobin, tissues, muscles, bone marrow, blood proteins, enzymes, ferritin, hemosiderin, and transport in plasma. The mechanical properties of iron and its alloys can be evaluated using a variety of tests, including the Brinell test, Rockwell test, the data on iron is so consistent that it is often used to calibrate measurements or to compare tests. An increase in the content will cause a significant increase in the hardness. Maximum hardness of 65 Rc is achieved with a 0. 6% carbon content, because of the softness of iron, it is much easier to work with than its heavier congeners ruthenium and osmium. Because of its significance for planetary cores, the properties of iron at high pressures and temperatures have also been studied extensively
