Redox is a chemical reaction in which the oxidation states of atoms are changed. Any such reaction involves both a process and a complementary oxidation process, two key concepts involved with electron transfer processes. Redox reactions include all chemical reactions in which atoms have their oxidation state changed, in general, the chemical species from which the electron is stripped is said to have been oxidized, while the chemical species to which the electron is added is said to have been reduced. It can be explained in terms, Oxidation is the loss of electrons or an increase in oxidation state by a molecule, atom. Reduction is the gain of electrons or a decrease in state by a molecule, atom. As an example, during the combustion of wood, oxygen from the air is reduced, the reaction can occur relatively slowly, as in the case of rust, or more quickly, as in the case of fire. Redox is a portmanteau of reduction and oxidation, the word oxidation originally implied reaction with oxygen to form an oxide, since dioxygen was historically the first recognized oxidizing agent.
Later, the term was expanded to encompass oxygen-like substances that accomplished parallel chemical reactions, the meaning was generalized to include all processes involving loss of electrons. The word reduction originally referred to the loss in weight upon heating a metallic ore such as an oxide to extract the metal. In other words, ore was reduced to metal, antoine Lavoisier showed that this loss of weight was due to the loss of oxygen as a gas. Later, scientists realized that the atom gains electrons in this process. The meaning of reduction became generalized to all processes involving gain of electrons. Even though reduction seems counter-intuitive when speaking of the gain of electrons, it help to think of reduction as the loss of oxygen. Since electrons are charged, it is helpful to think of this as reduction in electrical charge. The electrochemist John Bockris has used the words electronation and deelectronation to describe reduction and oxidation processes respectively when they occur at electrodes and these words are analogous to protonation and deprotonation, but they have not been widely adopted by chemists.
The term hydrogenation could be used instead of reduction, since hydrogen is the agent in a large number of reactions. But, unlike oxidation, which has been generalized beyond its root element, the word redox was first used in 1928. The processes of oxidation and reduction occur simultaneously and cannot happen independently of one another, the oxidation alone and the reduction alone are each called a half-reaction, because two half-reactions always occur together to form a whole reaction
Solubility is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a solid, liquid, or gaseous solvent. The solubility of a substance depends on the physical and chemical properties of the solute and solvent as well as on temperature, pressure. The solubility of a substance is a different property from the rate of solution. Most often, the solvent is a liquid, which can be a substance or a mixture. One may speak of solid solution, but rarely of solution in a gas, the extent of solubility ranges widely, from infinitely soluble such as ethanol in water, to poorly soluble, such as silver chloride in water. The term insoluble is often applied to poorly or very poorly soluble compounds, a common threshold to describe something as insoluble is less than 0.1 g per 100 mL of solvent. Under certain conditions, the solubility can be exceeded to give a so-called supersaturated solution. Metastability of crystals can lead to apparent differences in the amount of a chemical that dissolves depending on its form or particle size. A supersaturated solution generally crystallises when seed crystals are introduced and rapid equilibration occurs, phenylsalicylate is one such simple observable substance when fully melted and cooled below its fusion point.
Solubility is not to be confused with the ability to dissolve a substance, for example, zinc dissolves in hydrochloric acid as a result of a chemical reaction releasing hydrogen gas in a displacement reaction. The zinc ions are soluble in the acid, the smaller a particle is, the faster it dissolves although there are many factors to add to this generalization. Crucially solubility applies to all areas of chemistry, inorganic, organic, in all cases it will depend on the physical conditions and the enthalpy and entropy directly relating to the solvents and solutes concerned. By far the most common solvent in chemistry is water which is a solvent for most ionic compounds as well as a range of organic substances. This is a factor in acidity/alkalinity and much environmental and geochemical work. According to the IUPAC definition, solubility is the composition of a saturated solution expressed as a proportion of a designated solute in a designated solvent. Solubility may be stated in units of concentration such as molarity, mole fraction, mole ratio, mass per volume.
Solubility occurs under dynamic equilibrium, which means that solubility results from the simultaneous and opposing processes of dissolution, the solubility equilibrium occurs when the two processes proceed at a constant rate. The term solubility is used in some fields where the solute is altered by solvolysis
South Africa, officially the Republic of South Africa, is the southernmost country in Africa. South Africa is the 25th-largest country in the world by land area and it is the southernmost country on the mainland of the Old World or the Eastern Hemisphere. About 80 percent of South Africans are of Sub-Saharan African ancestry, divided among a variety of ethnic groups speaking different Bantu languages, the remaining population consists of Africas largest communities of European and multiracial ancestry. South Africa is a multiethnic society encompassing a variety of cultures, languages. Its pluralistic makeup is reflected in the recognition of 11 official languages. The country is one of the few in Africa never to have had a coup détat, the vast majority of black South Africans were not enfranchised until 1994. During the 20th century, the black majority sought to recover its rights from the dominant white minority, with this struggle playing a role in the countrys recent history. The National Party imposed apartheid in 1948, institutionalising previous racial segregation, since 1994, all ethnic and linguistic groups have held political representation in the countrys democracy, which comprises a parliamentary republic and nine provinces.
South Africa is often referred to as the Rainbow Nation to describe the multicultural diversity. The World Bank classifies South Africa as an economy. Its economy is the second-largest in Africa, and the 34th-largest in the world, in terms of purchasing power parity, South Africa has the seventh-highest per capita income in Africa. However and inequality remain widespread, with about a quarter of the population unemployed, South Africa has been identified as a middle power in international affairs, and maintains significant regional influence. The name South Africa is derived from the geographic location at the southern tip of Africa. Upon formation the country was named the Union of South Africa in English, since 1961 the long form name in English has been the Republic of South Africa. In Dutch the country was named Republiek van Zuid-Afrika, replaced in 1983 by the Afrikaans Republiek van Suid-Afrika, since 1994 the Republic has had an official name in each of its 11 official languages. Mzansi, derived from the Xhosa noun umzantsi meaning south, is a name for South Africa.
South Africa contains some of the oldest archaeological and human fossil sites in the world, extensive fossil remains have been recovered from a series of caves in Gauteng Province. The area is a UNESCO World Heritage site and has termed the Cradle of Humankind
Light is electromagnetic radiation within a certain portion of the electromagnetic spectrum. The word usually refers to light, which is visible to the human eye and is responsible for the sense of sight. Visible light is defined as having wavelengths in the range of 400–700 nanometres, or 4.00 × 10−7 to 7.00 × 10−7 m. This wavelength means a range of roughly 430–750 terahertz. The main source of light on Earth is the Sun, sunlight provides the energy that green plants use to create sugars mostly in the form of starches, which release energy into the living things that digest them. This process of photosynthesis provides virtually all the used by living things. Historically, another important source of light for humans has been fire, with the development of electric lights and power systems, electric lighting has effectively replaced firelight. Some species of animals generate their own light, a process called bioluminescence, for example, fireflies use light to locate mates, and vampire squids use it to hide themselves from prey.
Visible light, as all types of electromagnetic radiation, is experimentally found to always move at this speed in a vacuum. In physics, the term sometimes refers to electromagnetic radiation of any wavelength. In this sense, gamma rays, X-rays and radio waves are light, like all types of light, visible light is emitted and absorbed in tiny packets called photons and exhibits properties of both waves and particles. This property is referred to as the wave–particle duality, the study of light, known as optics, is an important research area in modern physics. Generally, EM radiation, or EMR, is classified by wavelength into radio, infrared, the behavior of EMR depends on its wavelength. Higher frequencies have shorter wavelengths, and lower frequencies have longer wavelengths, when EMR interacts with single atoms and molecules, its behavior depends on the amount of energy per quantum it carries. There exist animals that are sensitive to various types of infrared, infrared sensing in snakes depends on a kind of natural thermal imaging, in which tiny packets of cellular water are raised in temperature by the infrared radiation. EMR in this range causes molecular vibration and heating effects, which is how these animals detect it, above the range of visible light, ultraviolet light becomes invisible to humans, mostly because it is absorbed by the cornea below 360 nanometers and the internal lens below 400.
Furthermore, the rods and cones located in the retina of the eye cannot detect the very short ultraviolet wavelengths and are in fact damaged by ultraviolet. Many animals with eyes that do not require lenses are able to detect ultraviolet, by quantum photon-absorption mechanisms, various sources define visible light as narrowly as 420 to 680 to as broadly as 380 to 800 nm
Various forms of life exist, such as plants, fungi, protists and bacteria. The criteria can at times be ambiguous and may or may not define viruses, biology is the primary science concerned with the study of life, although many other sciences are involved. The definition of life is controversial, the current definition is that organisms maintain homeostasis, are composed of cells, undergo metabolism, can grow, adapt to their environment, respond to stimuli, and reproduce. However, many other definitions have been proposed, and there are some borderline cases. Modern definitions are more complex, with input from a diversity of scientific disciplines, biophysicists have proposed many definitions based on chemical systems, there are some living systems theories, such as the Gaia hypothesis, the idea that the Earth itself is alive. Another theory is that life is the property of systems, and yet another is elaborated in complex systems biology. Abiogenesis describes the process of life arising from non-living matter.
Properties common to all organisms include the need for certain chemical elements to sustain biochemical functions. Life on Earth first appeared as early as 4.28 billion years ago, soon after ocean formation 4.41 billion years ago, Earths current life may have descended from an RNA world, although RNA-based life may not have been the first. The mechanism by which began on Earth is unknown, though many hypotheses have been formulated and are often based on the Miller–Urey experiment. The earliest known forms are microfossils of bacteria. In July 2016, scientists reported identifying a set of 355 genes believed to be present in the last universal ancestor of all living organisms. Since its primordial beginnings, life on Earth has changed its environment on a time scale. To survive in most ecosystems, life must often adapt to a range of conditions. Some microorganisms, called extremophiles, thrive in physically or geochemically extreme environments that are detrimental to most other life on Earth, Aristotle was the first person to classify organisms.
Later, Carl Linnaeus introduced his system of nomenclature for the classification of species. Eventually new groups and categories of life were discovered, such as cells and microorganisms, cells are sometimes considered the smallest units and building blocks of life. There are two kinds of cells and eukaryotic, both of which consist of cytoplasm enclosed within a membrane and contain many such as proteins
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, 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, all sorts of organisms and immortalised cell lines and methods for molecular cloning and DNA replication
Chlorine is a chemical element with symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the table and its properties are mostly intermediate between them. Chlorine is a gas at room temperature. It is an extremely reactive element and a strong oxidising agent, among the elements, it has the highest electron affinity, the most common compound of chlorine, sodium chloride, has been known since ancient times. Around 1630, chlorine gas was first synthesised in a chemical reaction, Carl Wilhelm Scheele wrote a description of chlorine gas in 1774, supposing it to be an oxide of a new element. In 1809, chemists suggested that the gas might be an element, and this was confirmed by Sir Humphry Davy in 1810. Because of its reactivity, all chlorine in the Earths crust is in the form of ionic chloride compounds. It is the second-most abundant halogen and twenty-first most abundant chemical element in Earths crust and these crustal deposits are nevertheless dwarfed by the huge reserves of chloride in seawater.
Elemental chlorine is produced from brine by electrolysis. The high oxidising potential of chlorine led to the development of commercial bleaches and disinfectants. As a common disinfectant, elemental chlorine and chlorine-generating compounds are used directly in swimming pools to keep them clean. Elemental chlorine at high concentrations is extremely dangerous and poisonous for all living organisms, in the form of chloride ions, chlorine is necessary to all known species of life. Other types of compounds are rare in living organisms. In the upper atmosphere, chlorine-containing organic molecules such as chlorofluorocarbons have been implicated in ozone depletion, small quantities of elemental chlorine are generated by oxidation of chloride to hypochlorite in neutrophils as part of the immune response against bacteria. Its importance in food was very well known in antiquity and was sometimes used as payment for services for Roman generals. Around 1630, chlorine was recognized as a gas by the Flemish chemist, the element was first studied in detail in 1774 by Swedish chemist Carl Wilhelm Scheele, and he is credited with the discovery.
He called it dephlogisticated muriatic acid air since it is a gas and he failed to establish chlorine as an element, mistakenly thinking that it was the oxide obtained from the hydrochloric acid. He named the new element within this oxide as muriaticum, in 1809, Joseph Louis Gay-Lussac and Louis-Jacques Thénard tried to decompose dephlogisticated muriatic acid air by reacting it with charcoal to release the free element muriaticum
In physics, the electronvolt is a unit of energy equal to approximately 1. 6×10−19 joules. By definition, it is the amount of energy gained by the charge of an electron moving across an electric potential difference of one volt. Thus it is 1 volt multiplied by the elementary charge, one electronvolt is equal to 6981160217662079999♠1. 6021766208×10−19 J. The electronvolt is not a SI unit, and its definition is empirical, like the elementary charge on which it is based, it is not an independent quantity but is equal to 1 J/C √2hα / μ0c0. It is a unit of energy within physics, widely used in solid state, nuclear. It is commonly used with the metric prefixes milli-, kilo-, in some older documents, and in the name Bevatron, the symbol BeV is used, which stands for billion electronvolts, it is equivalent to the GeV. By mass–energy equivalence, the electronvolt is a unit of mass and it is common in particle physics, where units of mass and energy are often interchanged, to express mass in units of eV/c2, where c is the speed of light in vacuum.
It is common to express mass in terms of eV as a unit of mass. The mass equivalent of 1 eV/c2 is 1 eV / c 2 = ⋅1 V2 =1.783 ×10 −36 kg. For example, an electron and a positron, each with a mass of 0.511 MeV/c2, the proton has a mass of 0.938 GeV/c2. In general, the masses of all hadrons are of the order of 1 GeV/c2, the unified atomic mass unit,1 gram divided by Avogadros number, is almost the mass of a hydrogen atom, which is mostly the mass of the proton. To convert to megaelectronvolts, use the formula,1 u =931.4941 MeV/c2 =0.9314941 GeV/c2, in high-energy physics, the electronvolt is often used as a unit of momentum. A potential difference of 1 volt causes an electron to gain an amount of energy and this gives rise to usage of eV as units of momentum, for the energy supplied results in acceleration of the particle. The dimensions of units are LMT−1. The dimensions of units are L2MT−2. Then, dividing the units of energy by a constant that has units of velocity. In the field of particle physics, the fundamental velocity unit is the speed of light in vacuum c.
Thus, dividing energy in eV by the speed of light, the fundamental velocity constant c is often dropped from the units of momentum by way of defining units of length such that the value of c is unity
Saint Petersburg State University
Saint Petersburg State University is a Russian federal state-owned higher education institution based in Saint Petersburg. It is the oldest and one of the largest universities in Russia, the university has two primary campuses, one on Vasilievsky Island and the other in Peterhof. During the Soviet period, it was known as Leningrad State University and it was named after Andrei Zhdanov in 1948. Saint Petersburg State University is the second best multi-faculty university in Russia after Moscow State University, the university has a reputation for having educated the majority of Russias political elite, these include presidents Vladimir Putin and Dimitry Medvedev, both of whom studied Law at the university. The university is Russias oldest university, founded in 1724 by Peter the Great, Saint Petersburg state university is included in all ratings and lists of the best universities in the world and is one of the leaders in all indicators in Russia. The university was the first from Russian universities to join The Coimbra Group and it is disputed by the university administration whether Saint Petersburg State University or Moscow State University is the oldest higher education institution in Russia.
The Petersburg Pedagogical Institute, renamed the Main Pedagogical Institute in 1814, was established in 1804, in 1823 most of the university moved from the Twelve Collegia to the southern part of the city beyond the Fontanka. In 1824 a modified version of the charter of Moscow University was adopted as the first charter of the Saint Petersburg Imperial University, in 1829 there were 19 full professors and 169 full-time and part-time students at the university. In 1830 Tsar Nicholas returned the building of the Twelve Collegia back to the university. In 1835 a new Charter of the Imperial Universities of Russia was approved, Pyotr Pletnyov was reappointed Rector and ultimately became the longest-serving rector of Saint Petersburg University. In 1855 Oriental studies were separated from the Faculty of History and Philology, in 1859–1861 female part-time students could attend lectures in the university. In 1861 there were 1,270 full-time and 167 part-time students in the university, of them 498 were in the Faculty of Law, many Russian, Georgian etc.
managers and scientists studied at the Faculty of law therefore. During 1861–1862 there was student unrest in the university, and it was closed twice during the year. The students were denied freedom of assembly and placed under police surveillance, after the unrest, in 1865, only 524 students remained. A decree of the Emperor Alexander II of Russia adopted on 18 February 1863 restored the right of the university assembly to elect the rector and it formed the new faculty of the theory and history of art as part of the faculty of history and philology. In March 1869, student unrest shook the university again but on a smaller scale, by 1869,2,588 students had graduated from the university. In 1880 the Ministry of National Enlightenment forbade students to marry, in 1882 another student unrest took place in the university. In 1884 a new Charter of the Imperial Russian Universities was adopted, on March 1,1887 a group of the university students was arrested while planning an attempt on the life of Alexander III of Russia
Thermal-neutron reactors are the most common type of nuclear reactor, and light-water reactors are the most common type of thermal-neutron reactor. There are three varieties of light-water reactors, the water reactor, the boiling water reactor. It is however the first aqueous homogeneous reactor and the first reactor using enriched uranium as fuel, the purpose of this experience was to determine the feasibility of a nuclear reactor using light water as a moderator and coolant, and cladded solid uranium as fuel. The results showed that, with an enriched uranium, criticality could be reached. This experience was the first practical step toward light-water reactor, after World War II and with the availability of enriched uranium, new concepts of reactor became feasible. In 1946, Eugene Wigner and Alvin Weinberg proposed and developed the concept of a reactor using enriched uranium as a fuel and this concept was proposed for a reactor whose purpose was to test the behavior of materials under neutron flux.
This reactor, the Material Testing Reactor, was built in Idaho at INL and this MTR mock-up, called the Low Intensity Test Reactor, reached criticality on February 4,1950 and was the worlds first light-water reactor. Immediately after the end of World War II the United States Navy started a program under the direction of Captain Hyman Rickover and it developed the first pressurized water reactors in the early 1950s, and led to the successful deployment of the first nuclear submarine, the USS Nautilus. The Soviet Union independently developed a version of the PWR in the late 1950s, while functionally very similar to the American effort, it has certain design distinctions from Western PWRs. Researcher Samuel Untermyer II led the effort to develop the BWR at the US National Reactor Testing Station in a series of tests called the BORAX experiments, LWRs can be subdivided into three categories – pressurized water reactors, boiling water reactors, and supercritical water reactors. West Germany was once a player with BWRs.
In addition, light-water reactors make up the vast majority of reactors that power naval nuclear-powered vessels, the reason for near exclusive LWR use aboard nuclear naval vessels is the level of inherent safety built into these types of reactors. This capability is known as a negative coefficient of reactivity. The nuclear reactor core is the portion of a reactor where the nuclear reactions take place. It mainly consists of fuel and control elements. The pencil-thin nuclear fuel rods, each about 12 feet long, are grouped by the hundreds in bundles called fuel assemblies, inside each fuel rod, pellets of uranium, or more commonly uranium oxide, are stacked end to end. The control elements, called control rods, are filled with pellets of substances like hafnium or cadmium that readily capture neutrons, when the control rods are lowered into the core, they absorb neutrons, which thus cannot take part in the chain reaction. On the converse, when the rods are lifted out of the way, more neutrons strike the fissile uranium-235 or plutonium-239 nuclei in nearby fuel rods
Integrated Authority File
The Integrated Authority File or GND is an international authority file for the organisation of personal names, subject headings and corporate bodies from catalogues. It is used mainly for documentation in libraries and increasingly by archives, the GND is managed by the German National Library in cooperation with various regional library networks in German-speaking Europe and other partners. The GND falls under the Creative Commons Zero license, the GND specification provides a hierarchy of high-level entities and sub-classes, useful in library classification, and an approach to unambiguous identification of single elements. It comprises an ontology intended for knowledge representation in the semantic web, available in the RDF format
A chemical bond is a lasting attraction between atoms that enables the formation of chemical compounds. The bond may result from the force of attraction between atoms with opposite charges, or through the sharing of electrons as in the covalent bonds. Since opposite charges attract via an electromagnetic force, the negatively charged electrons that are orbiting the nucleus. An electron positioned between two nuclei will be attracted to both of them, and the nuclei will be attracted toward electrons in this position and this attraction constitutes the chemical bond. This phenomenon limits the distance between nuclei and atoms in a bond, in general, strong chemical bonding is associated with the sharing or transfer of electrons between the participating atoms. All bonds can be explained by quantum theory, but, in practice, simplification rules allow chemists to predict the strength, the octet rule and VSEPR theory are two examples. Electrostatics are used to describe bond polarities and the effects they have on chemical substances, a chemical bond is an attraction between atoms.
This attraction may be seen as the result of different behaviors of the outermost or valence electrons of atoms and these behaviors merge into each other seamlessly in various circumstances, so that there is no clear line to be drawn between them. However it remains useful and customary to differentiate different types of bond, which result in different properties of condensed matter. In the simplest view of a covalent bond, one or more electrons are drawn into the space between the two atomic nuclei, energy is released by bond formation. This is not as a reduction in energy, because the attraction of the two electrons to the two protons is offset by the electron-electron and proton-proton repulsions. In a polar covalent bond, one or more electrons are shared between two nuclei. Such weak intermolecular bonds give organic molecular substances, such as waxes and oils, their soft bulk character, the melting points of such covalent polymers and networks increase greatly. In a simplified view of a bond, the bonding electron is not shared at all.
In this type of bond, the atomic orbital of one atom has a vacancy which allows the addition of one or more electrons. These newly added electrons potentially occupy a lower energy-state than they experience in a different atom, one nucleus offers a more tightly bound position to an electron than does another nucleus, with the result that one atom may transfer an electron to the other. This transfer causes one atom to assume a net charge. The bond results from electrostatic attraction between atoms and the atoms become positive or negatively charged ions, ionic bonds may be seen as extreme examples of polarization in covalent bonds