Compounds with the prefix perfluoro- are hydrocarbons, including those with heteroatoms, wherein all C-H bonds have been replaced by C-F bonds. Fluorocarbons and their derivatives are useful fluoropolymers, solvents, perfluoroalkanes are very stable because of the strength of the carbon–fluorine bond, one of the strongest in organic chemistry. Additionally, multiple carbon–fluorine bonds increase the strength and stability of other nearby carbon–fluorine bonds on the same geminal carbon, multiple carbon–fluorine bonds strengthen the skeletal carbon–carbon bonds from the inductive effect. Therefore, saturated fluorocarbons are more chemically and thermally stable than their corresponding hydrocarbon counterparts and they are susceptible to attack by very strong reductants, e. g. Birch reduction and very specialized organometallic complexes. Fluorocarbons are colorless and have high density, up to twice that of water. They are not miscible with most organic solvents, but are miscible with some hydrocarbons and they have very low solubility in water, and water has a very low solubility in them.
As the high electronegativity of fluorine reduces the polarizability of the atom, as a result, fluorocarbons have low intermolecular attractive forces and are lipophobic in addition to being hydrophobic and non-polar. Reflecting the weak intermolecular forces these compounds exhibit low viscosities when compared to liquids of similar boiling points, low surface tension, the low attractive forces in fluorocarbon liquids make them compressible and able to dissolve gas relatively well. There are five perfluoroalkane gases, tetrafluoromethane, octafluoropropane, perfluoro-n-butane and perfluoro-iso-butane, nearly all other fluoroalkanes are liquids, the most notable exception is perfluorocyclohexane, which sublimes at 51 °C. Fluorocarbons have low energies and high dielectric strengths. Perfluoroalkanes In the 1960s there was a lot of interest in fluorocarbons as anesthetics, fluorocarbons have been considered as fire extinguishants to replace CFCs. This extinguishing effect has been attributed to their heat capacity.
It has been suggested that an atmosphere containing a significant percentage of perfluorocarbons on a station or similar would prevent fires altogether. When combustion does occur, toxic fumes result, including carbonyl fluoride, carbon monoxide, perfluorocarbons dissolve relatively high volumes of gases. The high solubility of gases is attributed to the weak interactions in these fluorocarbon fluids. This table shows values for the fraction, x1, of nitrogen dissolved, calculated from the Ostwald coefficient. The development of the fluorocarbon industry coincided with World War II, prior to that, fluorocarbons were prepared by reaction of fluorine with the hydrocarbon, i. e. direct fluorination. Because C-C bonds are cleaved by fluorine, direct fluorination mainly affords smaller perfluorocarbons, such as tetrafluoromethane, hexafluoroethane
Accessible surface area
The accessible surface area or solvent-accessible surface area is the surface area of a biomolecule that is accessible to a solvent. Measurement of ASA is usually described in units of square Ångstroms, ASA was first described by Lee & Richards in 1971 and is sometimes called the Lee-Richards molecular surface. ASA is typically calculated using the rolling ball algorithm developed by Shrake & Rupley in 1973 and this algorithm uses a sphere of a particular radius to probe the surface of the molecule. The points are drawn at a water molecules estimated radius beyond the van der Waals radius, all points are checked against the surface of neighboring atoms to determine whether they are buried or accessible. The number of points accessible is multiplied by the portion of area each point represents to calculate the ASA. The choice of the probe radius does have an effect on the surface area, as using a smaller probe radius detects more surface details. A typical value is 1. 4Å, which approximates the radius of a water molecule, another factor that affects the results is the definition of the VDW radii of the atoms in the molecule under study.
For example, the molecule may often lack hydrogen atoms which are implicit in the structure, the hydrogen atoms may be implicitly included in the atomic radii of the heavy atoms, with a measure called the group radii. In addition, the number of points created on the van der Waals surface of each atom determines another aspect of discretization, the LCPO method uses a linear approximation of the two-body problem for a quicker analytical calculation of ASA. The approximations used in LCPO result in an error in the range of 1-3 Å², recently a method was presented that calculates ASA fast and analytically using a power diagram. Accessible surface area is used when calculating the transfer free energy required to move a biomolecule from aqueous solvent to a non-polar solvent such as a lipid environment. The LCPO method is used when calculating implicit solvent effects in the molecular dynamics software package AMBER. It is recently suggested that surface area can be used to improve prediction of protein secondary structure.
The ASA is closely related to the concept of the solvent-excluded surface and it is calculated in practice via a rolling-ball algorithm developed by Frederic Richards and implemented three-dimensionally by Michael Connolly in 1983 and Tim Richmond in 1984. Connolly spent several years perfecting the method. Richmond, Timothy J. solvent accessible surface area and excluded volume in proteins, Michael L. Computation of molecular volume. Connolly, M. L. Molecular interstitial skeleton and Applications of Molecular Surfaces. Blaney, J. M. Distance Geometry in Molecular Modeling, grant, J. A. Pickup, B. T
Electrowetting is the modification of the wetting properties of a surface with an applied electric field. The electrowetting behavior of mercury and other liquids on variably charged surfaces was probably first explained by Gabriel Lippmann in 1875 and was observed much earlier. Frumkin used surface charge to change the shape of water drops in 1936, the term electrowetting was first introduced in 1981 by G. Beni and S. Hackwood to describe an effect proposed for designing a new type of display device for which they received a patent. The use of a transistor in microfluidic circuits for manipulating chemical and biological fluids was first investigated by J. Later. Silver at the NIH, EWOD-based electrowetting was disclosed for single and immiscible fluids to move, hold, Electrowetting using an insulating layer on top of the bare electrodes was studied by Bruno Berge in 1993. Electrowetting on this surface is called electrowetting-on-dielectric to distinguish it from the conventional electrowetting on the bare electrode.
Microfluidic manipulation of liquids by electrowetting was demonstrated first with mercury droplets in water and with water in air, manipulation of droplets on a two-dimensional path was demonstrated later. If the liquid is discretized and programmably manipulated, the approach is called Digital Microfluidic Circuits or Digital Microfluidics, the phenomenon of electrowetting can be understood in terms of the forces that result from the applied electric field. The fringing field at the corners of the droplet tends to pull the droplet down onto the electrode, lowering the macroscopic contact angle. Alternatively, electrowetting can be viewed from a thermodynamic perspective, the chemical component is just the natural surface tension of the solid/electrolyte interface with no electric field. The electrical component is the energy stored in the capacitor formed between the conductor and the electrolyte, the simplest derivation of electrowetting behavior is given by considering its thermodynamic model.
The thermodynamic derivation proceeds as follows, surface charge is but one component of surface energy, and other components are certainly perturbed by induced charge. So, an explanation of electrowetting is unquantified, but it should not be surprising that these limits exist. It was recently shown by Klarman et al, within this framework it is predicted that reversed electrowetting is possible. This same paper further suggests that electrohydrodynamic instability may be the source of saturation, reverse electrowetting can be used to harvest energy via a mechanical-to-electrical engineering scheme. Another electrowetting configuration is electrowetting on liquid-infused film, the liquid-infused film is achieved by locking a liquid lubricant in a porous membrane through the delicate control of wetting properties of the liquid and solid phases. Meanwhile, the effect associated with the EWOLF can be tailored by manipulating the viscosity. Optoelectrowetting, and photoelectrowetting are both optically-induced electrowetting effects, by optically modulating the number of carriers in the space-charge region of the semiconductor, the contact angle of a liquid droplet can be altered in a continuous way
Inkjet printing is a type of computer printing that recreates a digital image by propelling droplets of ink onto paper, plastic, or other substrates. Inkjet printers are the most commonly used type of printer, the concept of inkjet printing originated in the 20th century, and the technology was first extensively developed in the early 1950s. Starting in the late 1970s inkjet printers that could reproduce digital images generated by computers were developed, mainly by Epson, Hewlett-Packard, in the worldwide consumer market, four manufacturers account for the majority of inkjet printer sales, Canon, HP, and Brother. The emerging ink jet material deposition market uses inkjet technologies, typically printheads using piezoelectric crystals, the technology has been extended and the ″ink″ can now comprise living cells, for creating biosensors and for tissue engineering. There are two main technologies in use in contemporary inkjet printers and Drop-on-demand, the continuous inkjet method is used commercially for marking and coding of products and packages.
In 1867 Lord Kelvin patented the syphon recorder, which recorded telegraph signals as a trace on paper using an ink jet nozzle deflected by a magnetic coil. The first commercial devices were introduced in 1951 by Siemens, the ink droplets are subjected to an electrostatic field created by a charging electrode as they form, the field varies according to the degree of drop deflection desired. This results in a controlled, variable electrostatic charge on each droplet, charged droplets are separated by one or more uncharged guard droplets to minimize electrostatic repulsion between neighbouring droplets. The more highly charged droplets are deflected to a greater degree, only a small fraction of the droplets is used to print, the majority being recycled. CIJ is one of the oldest ink jet technologies in use and is fairly mature, viscosity is monitored and a solvent is added to counteract solvent loss. Drop-on-demand is divided into thermal DOD and piezoelectric DOD, most consumer inkjet printers, including those from Canon, Hewlett-Packard, and Lexmark, use the thermal inkjet process.
Vaughts work started in late 1978 with a project to develop fast, low-cost printing, the team at HP found that thin-film resistors could produce enough heat to fire an ink droplet. Two years the HP and Canon teams found out about each others work, in the thermal inkjet process, the print cartridges consist of a series of tiny chambers, each containing a heater, all of which are constructed by photolithography. The inks involved are usually water-based and use either pigments or dyes as the colorant, the inks must have a volatile component to form the vapor bubble, otherwise droplet ejection cannot occur. As no special materials are required, the print head is generally cheaper to produce than in other inkjet technologies, most commercial and industrial inkjet printers and some consumer printers use a piezoelectric material in an ink-filled chamber behind each nozzle instead of a heating element. When a voltage is applied, the material changes shape, generating a pressure pulse in the fluid. A DOD process uses software that directs the heads to apply between zero and eight droplets of ink per dot, only where needed, piezo inkjet technology is often used on production lines to mark products.
For instance, the date is often applied to products with this technique, in this application the head is stationary
Biomimetics or biomimicry is the imitation of the models and elements of nature for the purpose of solving complex human problems. The terms biomimetics and biomimicry derive from Ancient Greek, βίος, life, a closely related field is bionics. Living organisms have evolved well-adapted structures and materials over time through natural selection. Biomimetics has given rise to new technologies inspired by biological solutions at macro, humans have looked at nature for answers to problems throughout our existence. Nature has solved engineering problems such as self-healing abilities, environmental exposure tolerance and resistance, self-assembly, one of the early examples of biomimicry was the study of birds to enable human flight. The Wright Brothers, who succeeded in flying the first heavier-than-air aircraft in 1903, Biomimetics was coined by the American biophysicist and polymath Otto Schmitt during the 1950s. It was during his research that he developed the Schmitt trigger by studying the nerves in squid.
He continued to focus on devices that mimic natural systems and by 1957 he had perceived a converse to the view of biophysics at that time. Biophysics is not so much a matter as it is a point of view. It is an approach to problems of biological science utilizing the theory, biophysics is a biologists approach to problems of physical science and engineering, although this aspect has largely been neglected. A similar term, bionics was coined by Jack E. Steele in 1960 at Wright-Patterson Air Force Base in Dayton, Steele defined bionics as the science of systems which have some function copied from nature, or which represent characteristics of natural systems or their analogues. The term bionic became associated with the use of electronically operated artificial body parts, because the term bionic took on the implication of supernatural strength, the scientific community in English speaking countries largely abandoned it. The term biomimicry appeared as early as 1982, Biomimicry was popularized by scientist and author Janine Benyus in her 1997 book Biomimicry, Innovation Inspired by Nature.
Biomimicry is defined in the book as a new science that studies natures models and imitates or takes inspiration from these designs, Benyus suggests looking to Nature as a Model and Mentor and emphasizes sustainability as an objective of biomimicry. Biomorphic mineralization is a technique that produces materials with morphologies and structures resembling those of living organisms by using bio-structures as templates for mineralization. Compared to other methods of production, biomorphic mineralization is facile, environmentally benign. Morpho butterfly wings contain microstructures that create its coloring effect through structural coloration rather than pigmentation, incident light waves are reflected at specific wavelengths to create vibrant colors due to multilayer interference, thin film interference, and scattering properties. The scales of these butterflies consist of such as ridges, cross-ribs, ridge-lamellae
The hydrophobic effect is the observed tendency of nonpolar substances to aggregate in aqueous solution and exclude water molecules. The hydrophobic effect is responsible for the separation of a mixture of oil, hence the hydrophobic effect is essential to life. Substances for which this effect is observed are known as hydrophobes, amphiphiles are molecules that have both hydrophobic and hydrophilic domains. Detergents are composed of amphiphiles that allow molecules to be solubilized in water by forming micelles. They are important to cell membranes composed of phospholipids that prevent the internal aqueous environment of a cell from mixing with external water. In the case of folding, the hydrophobic effect is important to understanding the structure of proteins that have hydrophobic amino acids clustered together within the protein. Structures of water-soluble proteins have a core in which side chains are buried from water. Charged and polar side chains are situated on the surface where they interact with surrounding water molecules.
In biochemistry, the effect can be used to separate mixtures of proteins based on their hydrophobicity. To achieve better separation, a salt may be added and its concentration decreased as the separation progresses, the origin of the hydrophobic effect is not fully understood. Some argue that the interaction is mostly an entropic effect originating from the disruption of highly dynamic hydrogen bonds between molecules of liquid water by the nonpolar solute. A hydrocarbon chain or a similar region of a large molecule is incapable of forming hydrogen bonds with water. Introduction of such a non-hydrogen bonding surface into water causes disruption of the hydrogen bonding network between water molecules, the water molecules that form the cage have restricted mobility. In the solvation shell of small particles, the restriction amounts to some 10%. For example, in the case of dissolved xenon at room temperature a mobility restriction of 30% has been found, this leads to significant losses in translational and rotational entropy of water molecules and makes the process unfavorable in terms of the free energy in the system.
By aggregating together, nonpolar molecules reduce the area exposed to water. The hydrophobic effect can be quantified by measuring the partition coefficients of non-polar molecules between water and non-polar solvents, the partition coefficients can be transformed to free energy of transfer which includes enthalpic and entropic components, ΔG = ΔH - TΔS. These components are determined by calorimetry
A plant cuticle is a protecting film covering the epidermis of leaves, young shoots and other aerial plant organs without periderm. It consists of lipid and hydrocarbon polymers impregnated with wax, and is synthesized exclusively by the epidermal cells, the plant cuticle is a layer of lipid polymer impregnated with waxes that is present on the outer surfaces of the primary organs of all vascular land plants. The cuticle is composed of an insoluble cuticular membrane impregnated by, cutin, a polyester polymer composed of inter-esterified omega hydroxy acids which are cross-linked by ester and epoxide bonds, is the best-known structural component of the cuticular membrane. The cuticle can contain a non-saponifiable hydrocarbon polymer known as Cutan, aerial organs of many plants, such as the leaves of the sacred lotus have ultra-hydrophobic and self-cleaning properties that have been described by Barthlott and Neinhuis. The lotus effect has applications in biomimetic technical materials, dehydration protection provided by a maternal cuticle improves offspring fitness in the moss Funaria hygrometrica. and in the sporophytes of all vascular plants.
The waxy sheet of cuticle functions in defense, forming a barrier that resists penetration by virus particles, bacterial cells
A dimer is an oligomer consisting of two structurally similar monomers joined by bonds that can be either strong or weak, covalent or intermolecular. The term homodimer is used when the two molecules are identical and heterodimer when they are not, the reverse of dimerisation is often called dissociation. Carboxylic acids form dimers by hydrogen bonding of the acidic hydrogen, for example, acetic acid forms a dimer in the gas phase, where the monomer units are held together by hydrogen bonds. Under special conditions, most OH-containing molecules form dimers, e. g. the water dimer, borane occurs as the dimer diborane, due to the high Lewis acidity of the boron center. Excimers and exciplexes are excited structures with a short lifetime, for example, noble gases do not form stable dimers, but do form the excimers Ar2*, Kr2* and Xe2* under high pressure and electrical stimulation. Molecular dimers are formed by the reaction of two identical compounds e. g. 2A → A-A. In this example, monomer A is said to dimerise to give the dimer A-A, an example is a diaminocarbene, which dimerise to give a tetraaminoethylene,2 C2 → 2C=C2 Carbenes are highly reactive and readily form bonds.
Dicyclopentadiene is a dimer of two cyclopentadiene molecules that have reacted in a Diels-Alder reaction to give the product. Upon heating, it cracks to give monomers, C10H12 →2 C5H6 Many nonmetallic elements occur as dimers, nitrogen, oxygen. Mercury occurs as a cation, formally a heterodimer. In the context of polymers, dimer refers to the degree of polymerization 2, regardless of the stoichiometry or condensation reactions. For example, cellobiose is a dimer of glucose, even though the formation reaction produces water, 2C6H12O6 → C12H22O11 + H2O Here, amino acids can form dimers, which are called dipeptides. An example is glycylglycine, consisting of two glycine molecules joined by a peptide bond, other examples are aspartame and carnosine. Pyrimidine dimers are formed by a reaction from pyrimidine DNA bases. This cross-linking causes DNA mutations, which can be carcinogenic, causing skin cancers, monomer Trimer Polymer Protein dimer IUPAC Gold Book definition
In chemistry, polarity is a separation of electric charge leading to a molecule or its chemical groups having an electric dipole or multipole moment. Polar molecules must contain polar bonds due to a difference in electronegativity between the bonded atoms, a polar molecule with two or more polar bonds must have an asymmetric geometry so that the bond dipoles do not cancel each other. Polar molecules interact through dipole–dipole intermolecular forces and hydrogen bonds, Polarity underlies a number of physical properties including surface tension and melting and boiling points. Not all atoms attract electrons with the same force, the amount of pull an atom exerts on its electrons is called its electronegativity. Atoms with high electronegativities – such as fluorine and nitrogen – exert a pull on electrons than atoms with lower electronegativities. In a bond, this leads to sharing of electrons between the atoms, as electrons will be drawn closer to the atom with the higher electronegativity.
Because electrons have a charge, the unequal sharing of electrons within a bond leads to the formation of an electric dipole. Because the amount of charge separated in such dipoles is usually smaller than a charge, they are called partial charges, denoted as δ+. These symbols were introduced by Christopher Kelk Ingold and Edith Hilda Ingold in 1926, the bond dipole moment is calculated by multiplying the amount of charge separated and the distance between the charges. These dipoles within molecules can interact with dipoles in other molecules, Bonds can fall between one of two extremes – being completely nonpolar or completely polar. A completely nonpolar bond occurs when the electronegativities are identical and therefore possess a difference of zero, a completely polar bond is more correctly called an ionic bond, and occurs when the difference between electronegativities is large enough that one atom actually takes an electron from the other. The terms polar and nonpolar are usually applied to covalent bonds, to determine the polarity of a covalent bond using numerical means, the difference between the electronegativity of the atoms is used.
Bond polarity is typically divided into three groups that are based on the difference in electronegativity between the two bonded atoms. He estimated that a difference of 1.7 corresponds to 50% ionic character, see dipole § Molecular dipoles. While the molecules can be described as covalent, nonpolar covalent, or ionic. However, the properties are typical of such molecules. A molecule is composed of one or more chemical bonds between molecular orbitals of different atoms, a polar molecule has a net dipole as a result of the opposing charges from polar bonds arranged asymmetrically. Water is an example of a polar molecule since it has a positive charge on one side
Chemistry is a branch of physical science that studies the composition, structure and change of matter. Chemistry is sometimes called the science because it bridges other natural sciences, including physics. For the differences between chemistry and physics see comparison of chemistry and physics, the history of chemistry can be traced to alchemy, which had been practiced for several millennia in various parts of the world. The word chemistry comes from alchemy, which referred to a set of practices that encompassed elements of chemistry, philosophy, astronomy, mysticism. An alchemist was called a chemist in popular speech, and the suffix -ry was added to this to describe the art of the chemist as chemistry, the modern word alchemy in turn is derived from the Arabic word al-kīmīā. In origin, the term is borrowed from the Greek χημία or χημεία and this may have Egyptian origins since al-kīmīā is derived from the Greek χημία, which is in turn derived from the word Chemi or Kimi, which is the ancient name of Egypt in Egyptian.
Alternately, al-kīmīā may derive from χημεία, meaning cast together, in retrospect, the definition of chemistry has changed over time, as new discoveries and theories add to the functionality of the science. The term chymistry, in the view of noted scientist Robert Boyle in 1661, in 1837, Jean-Baptiste Dumas considered the word chemistry to refer to the science concerned with the laws and effects of molecular forces. More recently, in 1998, Professor Raymond Chang broadened the definition of chemistry to mean the study of matter, early civilizations, such as the Egyptians Babylonians, Indians amassed practical knowledge concerning the arts of metallurgy and dyes, but didnt develop a systematic theory. Greek atomism dates back to 440 BC, arising in works by such as Democritus and Epicurus. In 50 BC, the Roman philosopher Lucretius expanded upon the theory in his book De rerum natura, unlike modern concepts of science, Greek atomism was purely philosophical in nature, with little concern for empirical observations and no concern for chemical experiments.
Work, particularly the development of distillation, continued in the early Byzantine period with the most famous practitioner being the 4th century Greek-Egyptian Zosimos of Panopolis. He formulated Boyles law, rejected the four elements and proposed a mechanistic alternative of atoms. Before his work, many important discoveries had been made, the Scottish chemist Joseph Black and the Dutchman J. B. English scientist John Dalton proposed the theory of atoms, that all substances are composed of indivisible atoms of matter. Davy discovered nine new elements including the alkali metals by extracting them from their oxides with electric current, british William Prout first proposed ordering all the elements by their atomic weight as all atoms had a weight that was an exact multiple of the atomic weight of hydrogen. The inert gases, called the noble gases were discovered by William Ramsay in collaboration with Lord Rayleigh at the end of the century, thereby filling in the basic structure of the table.
Organic chemistry was developed by Justus von Liebig and others, following Friedrich Wöhlers synthesis of urea which proved that organisms were, in theory
Water is a transparent and nearly colorless chemical substance that is the main constituent of Earths streams and oceans, and the fluids of most living organisms. Its chemical formula is H2O, meaning that its molecule contains one oxygen, Water strictly refers to the liquid state of that substance, that prevails at standard ambient temperature and pressure, but it often refers to its solid state or its gaseous state. It occurs in nature as snow, ice packs and icebergs, fog, aquifers, Water covers 71% of the Earths surface. It is vital for all forms of life. Only 2. 5% of this water is freshwater, and 98. 8% of that water is in ice and groundwater. Less than 0. 3% of all freshwater is in rivers and the atmosphere, a greater quantity of water is found in the earths interior. Water on Earth moves continually through the cycle of evaporation and transpiration, precipitation. Evaporation and transpiration contribute to the precipitation over land, large amounts of water are chemically combined or adsorbed in hydrated minerals.
Safe drinking water is essential to humans and other even though it provides no calories or organic nutrients. There is a correlation between access to safe water and gross domestic product per capita. However, some observers have estimated that by 2025 more than half of the population will be facing water-based vulnerability. A report, issued in November 2009, suggests that by 2030, in developing regions of the world. Water plays an important role in the world economy, approximately 70% of the freshwater used by humans goes to agriculture. Fishing in salt and fresh water bodies is a source of food for many parts of the world. Much of long-distance trade of commodities and manufactured products is transported by boats through seas, lakes, large quantities of water and steam are used for cooling and heating, in industry and homes. Water is an excellent solvent for a variety of chemical substances, as such it is widely used in industrial processes. Water is central to many sports and other forms of entertainment, such as swimming, pleasure boating, boat racing, sport fishing, Water is a liquid at the temperatures and pressures that are most adequate for life.
Specifically, at atmospheric pressure of 1 bar, water is a liquid between the temperatures of 273.15 K and 373.15 K
In statistical thermodynamics, entropy is a measure of the number of microscopic configurations Ω that a thermodynamic system can have when in a state as specified by some macroscopic variables. Formally, S = k B ln Ω, for example, gas in a container with known volume and temperature could have an enormous number of possible configurations of the collection of individual gas molecules. Each instantaneous configuration of the gas may be regarded as random, Entropy may be understood as a measure of disorder within a macroscopic system. The second law of thermodynamics states that an isolated systems entropy never decreases, such systems spontaneously evolve towards thermodynamic equilibrium, the state with maximum entropy. Non-isolated systems may lose entropy, provided their environments entropy increases by at least that amount, since entropy is a function of the state of the system, a change in entropy of a system is determined by its initial and final states. This applies whether the process is reversible or irreversible, irreversible processes increase the combined entropy of the system and its environment.
The above definition is called the macroscopic definition of entropy because it can be used without regard to any microscopic description of the contents of a system. The concept of entropy has found to be generally useful and has several other formulations. Entropy was discovered when it was noticed to be a quantity that behaves as a function of state and it has the dimension of energy divided by temperature, which has a unit of joules per kelvin in the International System of Units. But the entropy of a substance is usually given as an intensive property—either entropy per unit mass or entropy per unit amount of substance. In statistical mechanics this reflects that the state of a system is generally non-degenerate. Understanding the role of entropy in various processes requires an understanding of how. It is often said that entropy is an expression of the disorder, or randomness of a system, the second law is now often seen as an expression of the fundamental postulate of statistical mechanics through the modern definition of entropy.
In other words, in any natural process there exists an inherent tendency towards the dissipation of useful energy and he made the analogy with that of how water falls in a water wheel. This was an insight into the second law of thermodynamics. g. Clausius described entropy as the transformation-content, i. e. dissipative energy use and this was in contrast to earlier views, based on the theories of Isaac Newton, that heat was an indestructible particle that had mass. Later, scientists such as Ludwig Boltzmann, Josiah Willard Gibbs, the essential problem in statistical thermodynamics, i. e. according to Erwin Schrödinger, has been to determine the distribution of a given amount of energy E over N identical systems. Carathéodory linked entropy with a definition of irreversibility, in terms of trajectories