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85-667: The Faraday Society was a British society for the study of physical chemistry , founded in 1903 and named in honour of Michael Faraday . In 1980, it merged with several similar organisations, including the Chemical Society , the Royal Institute of Chemistry , and the Society for Analytical Chemistry to form the Royal Society of Chemistry which is both a learned society and a professional body. At that time,

170-533: A Greek mathematician, linked entropy with a mathematical definition of irreversibility, in terms of trajectories and integrability. In 1865, Clausius named the concept of "the differential of a quantity which depends on the configuration of the system", entropy ( Entropie ) after the Greek word for 'transformation'. He gave "transformational content" ( Verwandlungsinhalt ) as a synonym, paralleling his "thermal and ergonal content" ( Wärme- und Werkinhalt ) as

255-695: A central concept for the first law of thermodynamics . Finally, a comparison of both the representations of a work output in a Carnot cycle gives us: | Q H | T H − | Q C | T C = Q H T H + Q C T C = 0 {\displaystyle {\frac {\left\vert Q_{\mathsf {H}}\right\vert }{T_{\mathsf {H}}}}-{\frac {\left\vert Q_{\mathsf {C}}\right\vert }{T_{\mathsf {C}}}}={\frac {Q_{\mathsf {H}}}{T_{\mathsf {H}}}}+{\frac {Q_{\mathsf {C}}}{T_{\mathsf {C}}}}=0} Similarly to

340-529: A cold one. If we consider a heat engine which is less effective than Carnot cycle (i.e., the work W {\textstyle W} produced by this engine is less than the maximum predicted by Carnot's theorem), its work output is capped by Carnot efficiency as: W < ( 1 − T C T H ) Q H {\displaystyle W<\left(1-{\frac {T_{\mathsf {C}}}{T_{\mathsf {H}}}}\right)Q_{\mathsf {H}}} Substitution of

425-459: A few concentrations and a temperature, instead of needing to know all the positions and speeds of every molecule in a mixture, is a special case of another key concept in physical chemistry, which is that to the extent an engineer needs to know, everything going on in a mixture of very large numbers (perhaps of the order of the Avogadro constant , 6 x 10 ) of particles can often be described by just

510-431: A few variables like pressure, temperature, and concentration. The precise reasons for this are described in statistical mechanics , a specialty within physical chemistry which is also shared with physics. Statistical mechanics also provides ways to predict the properties we see in everyday life from molecular properties without relying on empirical correlations based on chemical similarities. The term "physical chemistry"

595-429: A given chemical mixture. This is studied in chemical thermodynamics , which sets limits on quantities like how far a reaction can proceed, or how much energy can be converted into work in an internal combustion engine , and which provides links between properties like the thermal expansion coefficient and rate of change of entropy with pressure for a gas or a liquid . It can frequently be used to assess whether

680-676: A macroscopic perspective, in classical thermodynamics the entropy is interpreted as a state function of a thermodynamic system : that is, a property depending only on the current state of the system, independent of how that state came to be achieved. In any process, where the system gives up Δ E {\displaystyle \Delta E} of energy to the surrounding at the temperature T {\textstyle T} , its entropy falls by Δ S {\textstyle \Delta S} and at least T ⋅ Δ S {\textstyle T\cdot \Delta S} of that energy must be given up to

765-420: A reactor or engine design is feasible, or to check the validity of experimental data. To a limited extent, quasi-equilibrium and non-equilibrium thermodynamics can describe irreversible changes. However, classical thermodynamics is mostly concerned with systems in equilibrium and reversible changes and not what actually does happen, or how fast, away from equilibrium. Which reactions do occur and how fast

850-440: A reversible path between the same two states. However, the heat transferred to or from the surroundings is different as well as its entropy change. We can calculate the change of entropy only by integrating the above formula. To obtain the absolute value of the entropy, we consider the third law of thermodynamics : perfect crystals at the absolute zero have an entropy S = 0 {\textstyle S=0} . From

935-408: A sequence of elementary reactions , each with its own transition state. Key questions in kinetics include how the rate of reaction depends on temperature and on the concentrations of reactants and catalysts in the reaction mixture, as well as how catalysts and reaction conditions can be engineered to optimize the reaction rate. The fact that how fast reactions occur can often be specified with just

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1020-495: A small portion of heat δ Q r e v {\textstyle \delta Q_{\mathsf {rev}}} transferred to the system during reversible process divided by the temperature T {\textstyle T} of the system during this heat transfer : d S = δ Q r e v T {\displaystyle \mathrm {d} S={\frac {\delta Q_{\mathsf {rev}}}{T}}} The reversible process

1105-430: A state of thermodynamic equilibrium , which essentially are state variables . State variables depend only on the equilibrium condition, not on the path evolution to that state. State variables can be functions of state, also called state functions , in a sense that one state variable is a mathematical function of other state variables. Often, if some properties of a system are determined, they are sufficient to determine

1190-418: A system — modeled at first classically, e.g. Newtonian particles constituting a gas, and later quantum-mechanically (photons, phonons , spins, etc.). The two approaches form a consistent, unified view of the same phenomenon as expressed in the second law of thermodynamics, which has found universal applicability to physical processes. Many thermodynamic properties are defined by physical variables that define

1275-430: A violation of the second law of thermodynamics, since he does not possess information about variable X {\textstyle X} and its influence on the system. In other words, one must choose a complete set of macroscopic variables to describe the system, i.e. every independent parameter that may change during experiment. Entropy can also be defined for any Markov processes with reversible dynamics and

1360-491: A word that meant the same thing to everybody: nothing". Any method involving the notion of entropy, the very existence of which depends on the second law of thermodynamics, will doubtless seem to many far-fetched, and may repel beginners as obscure and difficult of comprehension. Willard Gibbs , Graphical Methods in the Thermodynamics of Fluids The concept of entropy is described by two principal approaches,

1445-493: Is quasistatic (i.e., it occurs without any dissipation, deviating only infinitesimally from the thermodynamic equilibrium), and it may conserve total entropy. For example, in the Carnot cycle , while the heat flow from a hot reservoir to a cold reservoir represents the increase in the entropy in a cold reservoir, the work output, if reversibly and perfectly stored, represents the decrease in the entropy which could be used to operate

1530-407: Is a density matrix , t r {\displaystyle \mathrm {tr} } is a trace operator and ln {\displaystyle \ln } is a matrix logarithm . Density matrix formalism is not required if the system occurs to be in a thermal equilibrium so long as the basis states are chosen to be eigenstates of Hamiltonian . For most practical purposes it can be taken as

1615-562: Is a logarithmic measure for the system with a number of states, each with a probability p i {\textstyle p_{i}} of being occupied (usually given by the Boltzmann distribution ): S = − k B ∑ i p i ln ⁡ p i {\displaystyle S=-k_{\mathsf {B}}\sum _{i}{p_{i}\ln {p_{i}}}} where k B {\textstyle k_{\mathsf {B}}}

1700-576: Is a scientific concept that is most commonly associated with a state of disorder, randomness, or uncertainty. The term and the concept are used in diverse fields, from classical thermodynamics , where it was first recognized, to the microscopic description of nature in statistical physics , and to the principles of information theory . It has found far-ranging applications in chemistry and physics , in biological systems and their relation to life, in cosmology , economics , sociology , weather science , climate change , and information systems including

1785-406: Is a function of state makes it useful. In the Carnot cycle , the working fluid returns to the same state that it had at the start of the cycle, hence the change or line integral of any state function, such as entropy, over this reversible cycle is zero. The entropy change d S {\textstyle \mathrm {d} S} of a system excluding its surroundings can be well-defined as

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1870-456: Is a temperature difference between reservoirs. Originally, Carnot did not distinguish between heats Q H {\textstyle Q_{\mathsf {H}}} and Q C {\textstyle Q_{\mathsf {C}}} , as he assumed caloric theory to be valid and hence that the total heat in the system was conserved. But in fact, the magnitude of heat Q H {\textstyle Q_{\mathsf {H}}}

1955-452: Is greater than the magnitude of heat Q C {\textstyle Q_{\mathsf {C}}} . Through the efforts of Clausius and Kelvin , the work W {\textstyle W} done by a reversible heat engine was found to be the product of the Carnot efficiency (i.e., the efficiency of all reversible heat engines with the same pair of thermal reservoirs) and

2040-414: Is known that a work W > 0 {\textstyle W>0} produced by an engine over a cycle equals to a net heat Q Σ = | Q H | − | Q C | {\textstyle Q_{\Sigma }=\left\vert Q_{\mathsf {H}}\right\vert -\left\vert Q_{\mathsf {C}}\right\vert } absorbed over a cycle. Thus, with

2125-510: Is now known as heat) falls through a temperature difference, work or motive power can be produced from the actions of its fall from a hot to cold body. He used an analogy with how water falls in a water wheel . That was an early insight into the second law of thermodynamics . Carnot based his views of heat partially on the early 18th-century "Newtonian hypothesis" that both heat and light were types of indestructible forms of matter, which are attracted and repelled by other matter, and partially on

2210-406: Is one with a fixed volume, number of molecules, and internal energy, called a microcanonical ensemble . The most general interpretation of entropy is as a measure of the extent of uncertainty about a system. The equilibrium state of a system maximizes the entropy because it does not reflect all information about the initial conditions, except for the conserved variables. This uncertainty is not of

2295-576: Is that energy may not flow to and from an isolated system, but energy flow to and from a closed system is possible. Nevertheless, for both closed and isolated systems, and indeed, also in open systems, irreversible thermodynamics processes may occur. According to the Clausius equality , for a reversible cyclic thermodynamic process: ∮ δ Q r e v T = 0 {\displaystyle \oint {\frac {\delta Q_{\mathsf {rev}}}{T}}=0} which means

2380-567: Is the Boltzmann constant and the summation is performed over all possible microstates of the system. In case states are defined in a continuous manner, the summation is replaced by an integral over all possible states, or equivalently we can consider the expected value of the logarithm of the probability that a microstate is occupied: S = − k B ⟨ ln ⁡ p ⟩ {\displaystyle S=-k_{\mathsf {B}}\left\langle \ln {p}\right\rangle } This definition assumes

2465-405: Is the number of microstates whose energy equals to the one of the system. Usually, this assumption is justified for an isolated system in a thermodynamic equilibrium. Then in case of an isolated system the previous formula reduces to: S = k B ln ⁡ Ω {\displaystyle S=k_{\mathsf {B}}\ln {\Omega }} In thermodynamics, such a system

2550-439: Is the subject of chemical kinetics , another branch of physical chemistry. A key idea in chemical kinetics is that for reactants to react and form products , most chemical species must go through transition states which are higher in energy than either the reactants or the products and serve as a barrier to reaction. In general, the higher the barrier, the slower the reaction. A second is that most chemical reactions occur as

2635-566: Is zero too, since the inversion of a heat transfer direction means a sign inversion for the heat transferred during isothermal stages: − Q H T H − Q C T C = Δ S r , H + Δ S r , C = 0 {\displaystyle -{\frac {Q_{\mathsf {H}}}{T_{\mathsf {H}}}}-{\frac {Q_{\mathsf {C}}}{T_{\mathsf {C}}}}=\Delta S_{\mathsf {r,H}}+\Delta S_{\mathsf {r,C}}=0} Here we denote

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2720-433: The detailed balance property. In Boltzmann's 1896 Lectures on Gas Theory , he showed that this expression gives a measure of entropy for systems of atoms and molecules in the gas phase, thus providing a measure for the entropy of classical thermodynamics. Entropy arises directly from the Carnot cycle . It can also be described as the reversible heat divided by temperature. Entropy is a fundamental function of state. In

2805-517: The 1860s to 1880s with work on chemical thermodynamics , electrolytes in solutions, chemical kinetics and other subjects. One milestone was the publication in 1876 by Josiah Willard Gibbs of his paper, On the Equilibrium of Heterogeneous Substances . This paper introduced several of the cornerstones of physical chemistry, such as Gibbs energy , chemical potentials , and Gibbs' phase rule . The first scientific journal specifically in

2890-527: The Carnot efficiency Kelvin had to evaluate the ratio of the work output to the heat absorbed during the isothermal expansion with the help of the Carnot–Clapeyron equation, which contained an unknown function called the Carnot function. The possibility that the Carnot function could be the temperature as measured from a zero point of temperature was suggested by Joule in a letter to Kelvin. This allowed Kelvin to establish his absolute temperature scale. It

2975-534: The Faraday Division became one of six units within the Royal Society of Chemistry. The Faraday Society published Faraday Transactions from 1905 to 1971, when the Royal Society of Chemistry took over the publication. Of particular note were the conferences called Faraday Discussions , which were published under the same name. The publication includes the discussion of the paper as well as

3060-557: The French mathematician Lazare Carnot proposed that in any machine, the accelerations and shocks of the moving parts represent losses of moment of activity ; in any natural process there exists an inherent tendency towards the dissipation of useful energy. In 1824, building on that work, Lazare's son, Sadi Carnot , published Reflections on the Motive Power of Fire , which posited that in all heat-engines, whenever " caloric " (what

3145-467: The President of the Faraday Division of the amalgamated Royal Society of Chemistry from 1978 to 1979. Prior to the amalgamation, Tompkins received valuable assistance from D. A. Young , who became Editor as of 1977. Physical chemistry Physical chemistry, in contrast to chemical physics , is predominantly (but not always) a supra-molecular science, as the majority of the principles on which it

3230-518: The application of quantum mechanics to chemical problems, provides tools to determine how strong and what shape bonds are, how nuclei move, and how light can be absorbed or emitted by a chemical compound. Spectroscopy is the related sub-discipline of physical chemistry which is specifically concerned with the interaction of electromagnetic radiation with matter. Another set of important questions in chemistry concerns what kind of reactions can happen spontaneously and which properties are possible for

3315-541: The basis states to be picked in a way that there is no information on their relative phases. In a general case the expression is: S = − k B   t r ( ρ ^ × ln ⁡ ρ ^ ) {\displaystyle S=-k_{\mathsf {B}}\ \mathrm {tr} {\left({\hat {\rho }}\times \ln {\hat {\rho }}\right)}} where ρ ^ {\textstyle {\hat {\rho }}}

3400-410: The concept, providing an explanation and a deeper understanding of its nature. The interpretation of entropy in statistical mechanics is the measure of uncertainty, disorder, or mixedupness in the phrase of Gibbs , which remains about a system after its observable macroscopic properties, such as temperature, pressure and volume, have been taken into account. For a given set of macroscopic variables,

3485-403: The contemporary views of Count Rumford , who showed in 1789 that heat could be created by friction, as when cannon bores are machined. Carnot reasoned that if the body of the working substance, such as a body of steam, is returned to its original state at the end of a complete engine cycle , "no change occurs in the condition of the working body". The first law of thermodynamics , deduced from

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3570-440: The derivation of internal energy, this equality implies existence of a state function S {\textstyle S} with a change of d S = δ Q / T {\textstyle \mathrm {d} S=\delta Q/T} and which is conserved over an entire cycle. Clausius called this state function entropy . In addition, the total change of entropy in both thermal reservoirs over Carnot cycle

3655-450: The description of devices operating near the limit of de Broglie waves , e.g. photovoltaic cells , have to be consistent with quantum statistics . The thermodynamic definition of entropy was developed in the early 1850s by Rudolf Clausius and essentially describes how to measure the entropy of an isolated system in thermodynamic equilibrium with its parts. Clausius created the term entropy as an extensive thermodynamic variable that

3740-779: The development of calculation algorithms in the field of "additive physicochemical properties" (practically all physicochemical properties, such as boiling point, critical point, surface tension, vapor pressure, etc.—more than 20 in all—can be precisely calculated from chemical structure alone, even if the chemical molecule remains unsynthesized), and herein lies the practical importance of contemporary physical chemistry. See Group contribution method , Lydersen method , Joback method , Benson group increment theory , quantitative structure–activity relationship Some journals that deal with physical chemistry include Historical journals that covered both chemistry and physics include Annales de chimie et de physique (started in 1789, published under

3825-483: The dimension of energy divided by temperature, and the unit joule per kelvin (J/K) in the International System of Units (SI). To find the entropy difference between any two states of the system, the integral must be evaluated for some reversible path between the initial and final states. Since an entropy is a state function, the entropy change of the system for an irreversible path is the same as for

3910-446: The entropy change for a thermal reservoir by Δ S r , i = − Q i / T i {\textstyle \Delta S_{{\mathsf {r}},i}=-Q_{i}/T_{i}} , where i {\textstyle i} is either H {\textstyle {\mathsf {H}}} for a hot reservoir or C {\textstyle {\mathsf {C}}} for

3995-409: The entropy measures the degree to which the probability of the system is spread out over different possible microstates . In contrast to the macrostate, which characterizes plainly observable average quantities, a microstate specifies all molecular details about the system including the position and momentum of every molecule. The more such states are available to the system with appreciable probability,

4080-825: The everyday subjective kind, but rather the uncertainty inherent to the experimental method and interpretative model. The interpretative model has a central role in determining entropy. The qualifier "for a given set of macroscopic variables" above has deep implications when two observers use different sets of macroscopic variables. For example, consider observer A using variables U {\textstyle U} , V {\textstyle V} , W {\textstyle W} and observer B using variables U {\textstyle U} , V {\textstyle V} , W {\textstyle W} , X {\textstyle X} . If observer B changes variable X {\textstyle X} , then observer A will see

4165-579: The field of physical chemistry was the German journal, Zeitschrift für Physikalische Chemie , founded in 1887 by Wilhelm Ostwald and Jacobus Henricus van 't Hoff . Together with Svante August Arrhenius , these were the leading figures in physical chemistry in the late 19th century and early 20th century. All three were awarded the Nobel Prize in Chemistry between 1901 and 1909. Developments in

4250-445: The following decades include the application of statistical mechanics to chemical systems and work on colloids and surface chemistry , where Irving Langmuir made many contributions. Another important step was the development of quantum mechanics into quantum chemistry from the 1930s, where Linus Pauling was one of the leading names. Theoretical developments have gone hand in hand with developments in experimental methods, where

4335-536: The fundamental definition of entropy since all other formulae for S {\textstyle S} can be derived from it, but not vice versa. In what has been called the fundamental postulate in statistical mechanics , among system microstates of the same energy (i.e., degenerate microstates ) each microstate is assumed to be populated with equal probability p i = 1 / Ω {\textstyle p_{i}=1/\Omega } , where Ω {\textstyle \Omega }

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4420-438: The greater the entropy. In statistical mechanics, entropy is a measure of the number of ways a system can be arranged, often taken to be a measure of "disorder" (the higher the entropy, the higher the disorder). This definition describes the entropy as being proportional to the natural logarithm of the number of possible microscopic configurations of the individual atoms and molecules of the system ( microstates ) that could cause

4505-437: The heat Q C {\textstyle Q_{\mathsf {C}}} is transferred from a working gas to a cold reservoir at the constant temperature T C {\textstyle T_{\mathsf {C}}} during isothermal compression stage. According to Carnot's theorem , a heat engine with two thermal reservoirs can produce a work W {\textstyle W} if and only if there

4590-605: The heat Q H {\textstyle Q_{\mathsf {H}}} absorbed by a working body of the engine during isothermal expansion: W = T H − T C T H ⋅ Q H = ( 1 − T C T H ) Q H {\displaystyle W={\frac {T_{\mathsf {H}}-T_{\mathsf {C}}}{T_{\mathsf {H}}}}\cdot Q_{\mathsf {H}}=\left(1-{\frac {T_{\mathsf {C}}}{T_{\mathsf {H}}}}\right)Q_{\mathsf {H}}} To derive

4675-438: The heat engine in reverse, returning to the initial state; thus the total entropy change may still be zero at all times if the entire process is reversible. In contrast, irreversible process increases the total entropy of the system and surroundings. Any process that happens quickly enough to deviate from the thermal equilibrium cannot be reversible, the total entropy increases, and the potential for maximum work to be done during

4760-434: The heat-friction experiments of James Joule in 1843, expresses the concept of energy and its conservation in all processes; the first law, however, is unsuitable to separately quantify the effects of friction and dissipation . In the 1850s and 1860s, German physicist Rudolf Clausius objected to the supposition that no change occurs in the working body, and gave that change a mathematical interpretation, by questioning

4845-422: The hint that at each stage of the cycle the difference between a work and a net heat would be conserved, rather than a net heat itself. Which means there exists a state function U {\textstyle U} with a change of d U = δ Q − d W {\textstyle \mathrm {d} U=\delta Q-\mathrm {d} W} . It is called an internal energy and forms

4930-508: The line integral ∫ L δ Q r e v / T {\textstyle \int _{L}{\delta Q_{\mathsf {rev}}/T}} is path-independent . Thus we can define a state function S {\textstyle S} , called entropy : d S = δ Q r e v T {\displaystyle \mathrm {d} S={\frac {\delta Q_{\mathsf {rev}}}{T}}} Therefore, thermodynamic entropy has

5015-421: The link between the microscopic interactions, which fluctuate about an average configuration, to the macroscopically observable behavior, in form of a simple logarithmic law, with a proportionality constant , the Boltzmann constant , that has become one of the defining universal constants for the modern International System of Units (SI). In his 1803 paper Fundamental Principles of Equilibrium and Movement ,

5100-405: The macroscopic perspective of classical thermodynamics , and the microscopic description central to statistical mechanics . The classical approach defines entropy in terms of macroscopically measurable physical properties, such as bulk mass, volume, pressure, and temperature. The statistical definition of entropy defines it in terms of the statistics of the motions of the microscopic constituents of

5185-421: The making and breaking of those bonds. Predicting the properties of chemical compounds from a description of atoms and how they bond is one of the major goals of physical chemistry. To describe the atoms and bonds precisely, it is necessary to know both where the nuclei of the atoms are, and how electrons are distributed around them. Quantum chemistry , a subfield of physical chemistry especially concerned with

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5270-1333: The name given here from 1815 to 1914). Entropy Collective intelligence Collective action Self-organized criticality Herd mentality Phase transition Agent-based modelling Synchronization Ant colony optimization Particle swarm optimization Swarm behaviour Social network analysis Small-world networks Centrality Motifs Graph theory Scaling Robustness Systems biology Dynamic networks Evolutionary computation Genetic algorithms Genetic programming Artificial life Machine learning Evolutionary developmental biology Artificial intelligence Evolutionary robotics Reaction–diffusion systems Partial differential equations Dissipative structures Percolation Cellular automata Spatial ecology Self-replication Conversation theory Entropy Feedback Goal-oriented Homeostasis Information theory Operationalization Second-order cybernetics Self-reference System dynamics Systems science Systems thinking Sensemaking Variety Ordinary differential equations Phase space Attractors Population dynamics Chaos Multistability Bifurcation Rational choice theory Bounded rationality Entropy

5355-424: The name of U , but preferring the term entropy as a close parallel of the word energy , as he found the concepts nearly "analogous in their physical significance". This term was formed by replacing the root of ἔργον ('ergon', 'work') by that of τροπή ('tropy', 'transformation'). In more detail, Clausius explained his choice of "entropy" as a name as follows: I prefer going to the ancient languages for

5440-471: The name of that property as entropy . The word was adopted into the English language in 1868. Later, scientists such as Ludwig Boltzmann , Josiah Willard Gibbs , and James Clerk Maxwell gave entropy a statistical basis. In 1877, Boltzmann visualized a probabilistic way to measure the entropy of an ensemble of ideal gas particles, in which he defined entropy as proportional to the natural logarithm of

5525-464: The names of important scientific quantities, so that they may mean the same thing in all living tongues. I propose, therefore, to call S the entropy of a body, after the Greek word "transformation". I have designedly coined the word entropy to be similar to energy, for these two quantities are so analogous in their physical significance, that an analogy of denominations seems to me helpful. Leon Cooper added that in this way "he succeeded in coining

5610-478: The nature of the inherent loss of usable heat when work is done, e.g., heat produced by friction. He described his observations as a dissipative use of energy, resulting in a transformation-content ( Verwandlungsinhalt in German), of a thermodynamic system or working body of chemical species during a change of state . That was in contrast to earlier views, based on the theories of Isaac Newton , that heat

5695-491: The number of microstates such a gas could occupy. The proportionality constant in this definition, called the Boltzmann constant , has become one of the defining universal constants for the modern International System of Units (SI). Henceforth, the essential problem in statistical thermodynamics has been to determine the distribution of a given amount of energy E over N identical systems. Constantin Carathéodory ,

5780-634: The observed macroscopic state ( macrostate ) of the system. The constant of proportionality is the Boltzmann constant . The Boltzmann constant, and therefore entropy, have dimensions of energy divided by temperature, which has a unit of joules per kelvin (J⋅K ) in the International System of Units (or kg⋅m ⋅s ⋅K in terms of base units). The entropy of a substance is usually given as an intensive property — either entropy per unit mass (SI unit: J⋅K ⋅kg ) or entropy per unit amount of substance (SI unit: J⋅K ⋅mol ). Specifically, entropy

5865-567: The paper itself. At the meeting, more time is given to the discussion than to the author presenting the paper as the audience are given the papers prior to the meeting. These conferences continue to be run by the Royal Society of Chemistry . In addition to its presidents, key figures at the Faraday Society included George Stanley Withers Marlow , Secretary and Editor of the society from 1926 to 1948, and his successor Frederick Clifford Tompkins . Tompkins served as Editor until 1977, and as

5950-498: The process is lost. The concept of entropy arose from Rudolf Clausius 's study of the Carnot cycle which is a thermodynamic cycle performed by a Carnot heat engine as a reversible heat engine. In a Carnot cycle the heat Q H {\textstyle Q_{\mathsf {H}}} is transferred from a hot reservoir to a working gas at the constant temperature T H {\textstyle T_{\mathsf {H}}} during isothermal expansion stage and

6035-757: The sign convention for a heat Q {\textstyle Q} transferred in a thermodynamic process ( Q > 0 {\textstyle Q>0} for an absorption and Q < 0 {\textstyle Q<0} for a dissipation) we get: W − Q Σ = W − | Q H | + | Q C | = W − Q H − Q C = 0 {\displaystyle W-Q_{\Sigma }=W-\left\vert Q_{\mathsf {H}}\right\vert +\left\vert Q_{\mathsf {C}}\right\vert =W-Q_{\mathsf {H}}-Q_{\mathsf {C}}=0} Since this equality holds over an entire Carnot cycle, it gave Clausius

6120-400: The state of the system and thus other properties' values. For example, temperature and pressure of a given quantity of gas determine its state, and thus also its volume via the ideal gas law . A system composed of a pure substance of a single phase at a particular uniform temperature and pressure is determined, and is thus a particular state, and has a particular volume. The fact that entropy

6205-536: The study of any classical thermodynamic heat engine: other cycles, such as an Otto , Diesel or Brayton cycle , could be analyzed from the same standpoint. Notably, any machine or cyclic process converting heat into work (i.e., heat engine) that is claimed to produce an efficiency greater than the one of Carnot is not viable — due to violation of the second law of thermodynamics . For further analysis of sufficiently discrete systems, such as an assembly of particles, statistical thermodynamics must be used. Additionally,

6290-405: The system's surroundings as a heat. Otherwise, this process cannot go forward. In classical thermodynamics, the entropy of a system is defined if and only if it is in a thermodynamic equilibrium (though a chemical equilibrium is not required: for example, the entropy of a mixture of two moles of hydrogen and one mole of oxygen in standard conditions is well-defined). The statistical definition

6375-465: The term entropy from a Greek word for transformation . Austrian physicist Ludwig Boltzmann explained entropy as the measure of the number of possible microscopic arrangements or states of individual atoms and molecules of a system that comply with the macroscopic condition of the system. He thereby introduced the concept of statistical disorder and probability distributions into a new field of thermodynamics, called statistical mechanics , and found

6460-452: The transmission of information in telecommunication . Entropy is central to the second law of thermodynamics , which states that the entropy of an isolated system left to spontaneous evolution cannot decrease with time. As a result, isolated systems evolve toward thermodynamic equilibrium , where the entropy is highest. A consequence of the second law of thermodynamics is that certain processes are irreversible . The thermodynamic concept

6545-467: The use of different forms of spectroscopy , such as infrared spectroscopy , microwave spectroscopy , electron paramagnetic resonance and nuclear magnetic resonance spectroscopy , is probably the most important 20th century development. Further development in physical chemistry may be attributed to discoveries in nuclear chemistry , especially in isotope separation (before and during World War II), more recent discoveries in astrochemistry , as well as

6630-769: The work W {\textstyle W} as the net heat into the inequality above gives us: Q H T H + Q C T C < 0 {\displaystyle {\frac {Q_{\mathsf {H}}}{T_{\mathsf {H}}}}+{\frac {Q_{\mathsf {C}}}{T_{\mathsf {C}}}}<0} or in terms of the entropy change Δ S r , i {\textstyle \Delta S_{{\mathsf {r}},i}} : Δ S r , H + Δ S r , C > 0 {\displaystyle \Delta S_{\mathsf {r,H}}+\Delta S_{\mathsf {r,C}}>0} A Carnot cycle and an entropy as shown above prove to be useful in

6715-448: Was an indestructible particle that had mass. Clausius discovered that the non-usable energy increases as steam proceeds from inlet to exhaust in a steam engine. From the prefix en- , as in 'energy', and from the Greek word τροπή [tropē], which is translated in an established lexicon as turning or change and that he rendered in German as Verwandlung , a word often translated into English as transformation , in 1865 Clausius coined

6800-571: Was coined by Mikhail Lomonosov in 1752, when he presented a lecture course entitled "A Course in True Physical Chemistry" ( Russian : Курс истинной физической химии ) before the students of Petersburg University . In the preamble to these lectures he gives the definition: "Physical chemistry is the science that must explain under provisions of physical experiments the reason for what is happening in complex bodies through chemical operations". Modern physical chemistry originated in

6885-440: Was developed by Ludwig Boltzmann in the 1870s by analyzing the statistical behavior of the microscopic components of the system. Boltzmann showed that this definition of entropy was equivalent to the thermodynamic entropy to within a constant factor—known as the Boltzmann constant . In short, the thermodynamic definition of entropy provides the experimental verification of entropy, while the statistical definition of entropy extends

6970-515: Was found to vary in the thermodynamic cycle but eventually returned to the same value at the end of every cycle. Thus it was found to be a function of state , specifically a thermodynamic state of the system. While Clausius based his definition on a reversible process, there are also irreversible processes that change entropy. Following the second law of thermodynamics , entropy of an isolated system always increases for irreversible processes. The difference between an isolated system and closed system

7055-526: Was founded relate to the bulk rather than the molecular or atomic structure alone (for example, chemical equilibrium and colloids ). Some of the relationships that physical chemistry strives to understand include the effects of: The key concepts of physical chemistry are the ways in which pure physics is applied to chemical problems. One of the key concepts in classical chemistry is that all chemical compounds can be described as groups of atoms bonded together and chemical reactions can be described as

7140-523: Was referred to by Scottish scientist and engineer William Rankine in 1850 with the names thermodynamic function and heat-potential . In 1865, German physicist Rudolf Clausius , one of the leading founders of the field of thermodynamics, defined it as the quotient of an infinitesimal amount of heat to the instantaneous temperature. He initially described it as transformation-content , in German Verwandlungsinhalt , and later coined

7225-399: Was shown to be useful in characterizing the Carnot cycle . Heat transfer in the isotherm steps (isothermal expansion and isothermal compression) of the Carnot cycle was found to be proportional to the temperature of a system (known as its absolute temperature ). This relationship was expressed in an increment of entropy that is equal to incremental heat transfer divided by temperature. Entropy

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