In thermodynamics, the Gibbs free energy is a thermodynamic potential which measures the "useful" work obtainable from a closed thermodynamic system at a constant temperature and pressure. Under these conditions, it is zero at equilibrium. This article needs to be cleaned up to conform to a higher standard of quality. ... In thermodynamics, the internal energy of a thermodynamic system, or a body with well-defined boundaries, denoted by U, or sometimes E, is the total of the kinetic energy due to the motion of molecules (translational, rotational, vibrational) and the potential energy associated with the vibrational and electric energy of... The Helmholtz energy is a thermodynamic potential which measures the useful work obtainable from constant temperature, constant volume thermodynamic systems. ... Enthalpy (symbolized H, also called heat content) is the sum of the internal energy of matter and the product of its volume multiplied by the pressure. ... Thermodynamics (from the Greek thermos meaning heat and dynamics meaning power) is a branch of physics that studies the effects of changes in temperature, pressure, and volume on physical systems at the macroscopic scale by analyzing the collective motion of their particles using statistics. ... In thermodynamics, four quantities, measured in units of energy, are called thermodynamic potentials: where T = temperature, S = entropy, p = pressure, V = volume Differential definitions The following differential relations hold for the four potentials: If we write the above four equations generally as Then it is seen that yielding expressions for... In thermodynamics, a closed system, as contrasted with an isolated system, can exchange heat and work, but not matter, with its surroundings. ... Thermodynamics (Greek: thermos = heat and dynamic = change) is the physics of energy, heat, work, entropy and the spontaneity of processes. ...

The Gibbs free energy was developed in the 1870s by the American mathematical physicist Willard Gibbs. The Gibbs free energy is defined as: Josiah Willard Gibbs (February 11, 1839 – April 28, 1903) was an American mathematical physicist who contributed much of the theoretical foundation that led to the development of chemical thermodynamics and was one of the founders of vector analysis. ...

where (in SI units) Cover of brochure The International System of Units. ...

• G is the Gibbs energy (joules)
• H is the enthalpy (joules)
• T is the temperature (kelvins)
• S is the entropy (joules per kelvin)

Each quantity in the equation above can be divided by the amount of substance, measured in moles, to form molar Gibbs energy. The Gibbs energy is one of the most important thermodynamic functions for the characterization of a system. It is a factor in determining outcomes such as the voltage of an electrochemical cell, and the equilibrium constant for a reversible reaction. The Gibbs free energy, in addition, goes by various names such as: Gibbs energy function, free energy, free enthalpy, thermodynamic potential at constant pressure, and others. The joule (symbol: J) is the SI unit of energy, which is defined as the potential to do work. ... Enthalpy (symbolized H, also called heat content) is the sum of the internal energy of matter and the product of its volume multiplied by the pressure. ... [[Image:Translational motion. ... The Kelvin scale is a thermodynamic (absolute) temperature scale where absolute zero—the lowest possible temperature where nothing could be colder and no heat energy remains in a substance—is defined as zero kelvin (0 K). ... For other uses of the term entropy, see Entropy (disambiguation) The thermodynamic entropy S, often simply called the entropy in the context of thermodynamics, is a measure of the amount of energy in a physical system that cannot be used to do work. ... The mole (symbol: mol) is the SI base unit that measures an amount of substance. ... now. ... An electrochemical cell is a setup used for creating an electromotive force(voltage) in a conductor separating two reactions. ... In chemistry, the equilibrium constant is a quantity characterizing a chemical equilibrium in a chemical reaction which is a useful tool to determine the concentration of various reactants or products in a system where chemical equilibrium occurs. ... A reversible reaction is a chemical reaction that may proceed in both the forward and reverse directions. ...

Overview

In a simple manner, with respect to STP reacting systems, a general rule of thumb is: Temperature and air pressure can vary from one place to another on the Earth, and can also vary in the same place with time. ... A rule of thumb is an easily learned and easily applied procedure for approximately calculating or recalling some value, or for making some determination. ...

Every system seeks to achieve a minimum of free energy.

Hence, out of this general natural tendency, a quantitative measure as to how near or far a potential reaction is from this minimum is when the calculated energetics of the process indicate that the change in Gibbs free energy ΔG is negative. Essentially, this means that such a reaction will be favored and will release energy. The energy released equals the maximum amount of work that can be performed as a result of the chemical reaction. Conversely, if conditions indicated a positive ΔG, then energy--in the form of work--would have to be added to the reacting system to make the reaction go. Image File history File links Cquote1. ... Image File history File links Cquote2. ...

History

The quantity called "free energy" is essentially a more advanced and accurate replacement for the term “affinity” used by chemists, of olden days, to describe the “force” that caused chemical reactions. The term affinity, as used in chemical relation, dates back to at least the time of Albertus Magnus in 1250. Look up affinity in Wiktionary, the free dictionary. ... A chemical reaction occurs when vapours of hydrogen chloride and ammonia meet to form a cloud of a new substance, ammonium chloride Chemical reaction is a process that results in the interconversion of chemical substances [1]. The substance or substances initially involved in a chemical reaction are called reactants. ... Albertus Magnus (1193? – November 15, 1280), also known as Saint Albert the Great and Albert of Cologne, was a Dominican friar who became famous for his comprehensive knowledge and advocacy for the peaceful coexistence of science and religion. ...

From the 1998 textbook Modern Thermodynamics by Nobelist and chemical engineering professor Ilya Prigogine’s we find: “as motion was explained by the Newtonian concept of force, chemists wanted a similar concept of ‘driving force’ for chemical change? Why do chemical reactions occur, and why do they stop at certain points? Chemists called the ‘force’ that caused chemical reactions affinity, but it lacked a clear definition. Ilya Prigogine (January 25, 1917 – May 28, 2003) was a Belgian physicist and chemist noted for his work on dissipative structures, complex systems, and irreversibility. ...

During the entire 18th century, the dominant view in regards to heat and light was that put forward by Isaac Newton, called the “Newtonian hypothesis”, which stated that light and heat are forms of matter attracted or repelled by other forms of matter, with forces analogous to gravitation or to chemical affinity. Sir Isaac Newton, FRS (4 January 1643 – 31 March 1727) [ OS: 25 December 1642 – 20 March 1727][1] was an English physicist, mathematician, astronomer, alchemist, and natural philosopher, regarded by many as the greatest figure in the history of science. ...

In the 19th century, the French chemist Marcellin Berthelot and the Danish chemist Julius Thomsen had attempted to quantify affinity using heats of reaction. In 1875, after quantifying the heats of reaction for a large number of compounds, Berthelot proposed the “principle of maximum work” in which all chemical changes occurring without intervention of outside energy tend toward the production of bodies or of a system of bodies which liberate heat. Marcellin Berthelot Marcellin (or Marcelin) Pierre Eugène Berthelot (October 25, 1827 - March 18, 1907) was a French chemist and politician. ... Hans Peter Jörgen Julius Thomsen (February 16, 1826 – February 13, 1909) was a Danish chemist. ... The standard enthalpy change of reaction (denoted ΔH° or ΔHo)is the enthalpy change that occurs in a system when one mole of matter is transformed by a chemical reaction under standard conditions. ... In thermochemistry, the principle of maximum work was a postulate put forward in 1875 by the French chemist Marcellin Berthelot which stated that chemical reactions will tend to evolve in such a manner so as to assemble or dissasemble chemical species so to yield the maximum amount of chemical energy... In physics, heat, symbolized by Q, is defined as energy in transit. ...

In addition to this, in 1780 Antoine Lavoisier and Pierre-Simon Laplace laid the foundations of thermochemistry by showing that the heat evolved in a reaction is equal to the heat absorbed in the reverse reaction. They also investigated the specific heat and latent heat of a number of substances, and amounts of heat evolved in combustion. Similarly, in 1840 Swiss chemist Germain Hess formulated the principle that the evolution of heat in a reaction is the same whether the process is accomplished in one-step or in a number of stages. This known as Hess' law. With the advent of the mechanical theory of heat in the early 19th century, Hess’s law came to be viewed as a consequence of the law of conservation of energy. Antoine-Laurent de Lavoisier (August 26, 1743 – May 8, 1794) was a French nobleman prominent in the histories of chemistry, finance, biology, and economics. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... In the thermodynamics and physical chemistry, thermochemistry is the study of the heat evolved or absorbed in chemical reactions. ... The specific heat capacity (symbol c or s, also called specific heat) of a substance is defined as heat capacity per unit mass. ... This article or section does not cite its references or sources. ... Germain Henri Hess (1802-08-07 - 1850-11-30) was a Swiss chemist and doctor who formulated Hesss Law, an early principle of thermochemistry. ... Hess law states that the enthalpy change for a reaction will be the same as the enthalpy change of that reaction by any other pathway. ... In the history of science, the theory of heat or mechanical theory of heat was a theory, introduced predominately in 1824 by the French physicist Sadi Carnot, that heat and mechanical work are equivalent. ... Conservation of energy states that the total amount of energy (often expressed as the sum of kinetic energy and potential energy) in an isolated system remains constant. ...

Based on these and other ideas, Berthelot and Danish chemist Julius Thomsen, as well as others, considered the heat evolved in the formation of a compound as a measure of the affinity, or the work done by the chemical forces. This view, however, was not entirely correct. In 1847, the English physicist James Joule showed that he could raise the temperature of water by turning a paddle wheel in it, thus showing that heat and mechanical work were equivalent or proportional to each other, i.e. approximately, . This statement came to be known as the mechanical equivalent of heat and was a precursory form of the first law of thermodynamics. Hans Peter Jörgen Julius Thomsen (February 16, 1826 – February 13, 1909) was a Danish chemist. ... James Prescott Joule (December 24, 1818–October 11, 1889) was an English physicist, born in Salford, near Manchester. ... Conservation of energy also known as the first law of thermodynamics is possibly the most important, and certainly the most practically useful, of several conservation laws in physics. ... The first law of thermodynamics, a generalized expression of the law of the conservation of energy, states: // Description Essentially, the First Law of Thermodynamics declares that energy is conserved for a closed system, with heat and work being the forms of energy transfer. ...

By 1865, the German physicist Rudolf Clausius had showed that this equivalence principle needed amendment. That is, one can use the heat derived from a combustion reaction in a coal furnace to boil water, and use this heat to vaporize steam, and then use the enhanced high pressure energy of the vaporized steam to push a piston. Thus, we might naively reason that one can entirely convert the initial combustion heat of the chemical reaction into the work of pushing the piston. Clausius showed, however, that we need to take into account the work that the molecules of the working body, i.e. the water molecules in the cylinder, do on each other as they pass or transform from one step of or state of the engine cycle to the next, e.g. from (P1,V1) to (P2,V2). Clausius originally called this the “transformation content” of the body, and than later changed the name to entropy. Thus, the heat used to transform the working body of molecules from one state to the next cannot be used to do external work, e.g. to push the piston. Clausius defined this transformation heat as dQ = TdS. Rudolf Clausius - physicist and mathematician Rudolf Julius Emanuel Clausius (January 2, 1822 – August 24, 1888), was a German physicist and mathematician. ... Combustion or burning is a complex sequence of chemical reactions between a fuel and an oxidant accompanied by the production of heat or both heat and light in the form of either a glow or flames. ... This article needs to be cleaned up to conform to a higher standard of quality. ... The Carnot cycle is a particular thermodynamic cycle, modeled on the Carnot heat engine, studied by Nicolas Léonard Sadi Carnot in the 1820s and expanded upon by Benoit Paul Émile Clapeyron in the 1830s and 40s. ... In thermodynamics, entropy, symbolized by S, is a state function of a thermodynamic system defined by the differential quantity , where dQ is the amount of heat absorbed in a reversible process in which the system goes from the one state to another, and T is the absolute temperature. ...

In 1873, Willard Gibbs published A Method of Geometrical Representation of the Thermodynamic Properties of Substances by Means of Surfaces in which he introduced the preliminary outline of the principles of his new equation able to predict or estimate the tendencies of various natural processes to ensue when bodies or systems are brought into contact. By studying the interactions of homogeneous substances in contact, i.e. bodies, being in composition part solid, part liquid, and part vapor, and by using a three-dimensional volume-entropy-internal energy graph, Gibbs was able to determine three states of equilibrium, i.e. "necessarily stable", "neutral", and "unstable", and whether or not changes will ensue. In 1876, Gibbs built on this framework by introducing the concept of chemical potential so to take into account chemical reactions and states of bodies which are chemically different from each other. In his own words, to summarize his results in 1873, Gibbs states: Josiah Willard Gibbs (February 11, 1839 – April 28, 1903) was an American mathematical physicist who contributed much of the theoretical foundation that led to the development of chemical thermodynamics and was one of the founders of vector analysis. ... Volume is a quantification of how much space a certain region occupies. ... In thermodynamics, entropy, symbolized by S, is a state function of a thermodynamic system defined by the differential quantity , where dQ is the amount of heat absorbed in a reversible process in which the system goes from the one state to another, and T is the absolute temperature. ... In thermodynamics, the internal energy of a thermodynamic system, or a body with well-defined boundaries, denoted by U, or sometimes E, is the total of the kinetic energy due to the motion of molecules (translational, rotational, vibrational) and the potential energy associated with the vibrational and electric energy of... In thermodynamics and chemistry, chemical potential, symbolized by μ, is a term introduced in 1876 by the American mathematical physicist (Willard Gibbs and his partner Lauren Berkley), which he defined as follows: Gibbs noted also that for the purposes of this definition, any chemical element or combination of elements in given...

In this description, as used by Gibbs, ε refers to the internal energy of the body, η refers to the entropy of the body, and υ is the volume of the body. In thermodynamics, the internal energy of a thermodynamic system, or a body with well-defined boundaries, denoted by U, or sometimes E, is the total of the kinetic energy due to the motion of molecules (translational, rotational, vibrational) and the potential energy associated with the vibrational and electric energy of... In thermodynamics, entropy, symbolized by S, is a state function of a thermodynamic system defined by the differential quantity , where dQ is the amount of heat absorbed in a reversible process in which the system goes from the one state to another, and T is the absolute temperature. ... Volume is a quantification of how much space a certain region occupies. ...

Hence, in 1882, after the introduction of these arguments by Clausius and Gibbs, the German scientist Hermann von Helmholtz stated, in opposition to Berthelot and Thomas’ hypothesis that chemical affinity is a measure of the heat of reaction of chemical reaction as based on the principle of maximal work, that affinity is not the heat evolved in the formation of a compound but rather it is the largest quantity of work which can be gained when the reaction is carried out in a reversible manner, e.g. electrical work in a reversible cell. The maximum work is thus regarded as the diminution of the free, or available, energy of the system (Gibbs free energy G at T = constant, P = constant or Helmholtz free energy F at T = constant, V = constant), whilst the heat evolved is usually a measure of the diminution of the total energy of the system (Internal energy). Thus, G or F is the amount of energy “free” for work under the given conditions. Hermann von Helmholtz Hermann Ludwig Ferdinand von Helmholtz (August 31, 1821 – September 8, 1894) was a German physician and physicist. ... In thermodynamics, the internal energy of a thermodynamic system, or a body with well-defined boundaries, denoted by U, or sometimes E, is the total of the kinetic energy due to the motion of molecules (translational, rotational, vibrational) and the potential energy associated with the vibrational and electric energy of...

Up until this point, the general view had been such that: “all chemical reactions drive the system to a state of equilibrium in which the affinities of the reactions vanish”. Over the next 60 years, the term affinity came to be replaced with the term free energy. According to chemistry historian Henry Leicester, the influential 1923 textbook Thermodynamics and the Free Energy of Chemical Reactions by Gilbert N. Lewis and Merle Randall led to the replacement of the term “affinity” by the term “free energy” in much of the English-speaking world. Lewis in the Berkeley Lab Gilbert Newton Lewis (October 23, 1875-March 23, 1946) was a famous American physical chemist. ... Merle Randall was an American physical chemist famous for his work, over the period of 25 years, in measuring free energy calculations of compounds with Gilbert N. Lewis. ...

Why is the attachment ‘free’ so important?

In the 18th and 19th centuries, the theory of heat, i.e. that heat is a form of energy having relation to vibratory motion, was beginning to supplant both the caloric theory, i.e. that heat is a fluid, and the four element theory in which heat was the lightest of the four elements. Many textbooks and teaching articles during these centuries presented these theories side by side. Similarly, during these years, heat was beginning to be distinguished into different classification categories, such as “free heat”, “combined heat”, “radiant heat”, specific heat, heat capacity, “absolute heat”, “latent caloric”, “free” or “perceptible” caloric (calorique sensible), among others. In the history of science, the theory of heat was a term used during the 18th and 19th centuries to describe a number of laws, relations, and experimental phenomenon in relation to heat; those such as thermometry, calorimetry, combustion, specific heat, and discussions as to the quantity of heat released... The caloric theory is an obsolete scientific theory that heat consists of a fluid called caloric that flows from hotter to colder bodies. ... Chinese Wood (木) | Fire (火) Earth (土) | Metal (金) | Water (æ°´) Hinduism and Buddhism Vayu / Pavan — Air / Wind Agni / Tejas — Fire Akasha — Aether Prithvi / Bhumi — Earth Ap / Jala — Water Many ancient philosophies used a set of archetypal classical elements to explain patterns in nature. ... In physics, heat, symbolized by Q, is defined as energy in transit. ... The specific heat capacity (symbol c or s, also called specific heat) of a substance is defined as heat capacity per unit mass. ... To meet Wikipedias quality standards, this article or section may require cleanup. ...

In 1780, for example, Laplace and Lavoisier stated: “In general, one can change the first hypothesis into the second by changing the words ‘free heat, combined heat, and heat released’ into ‘vis viva, loss of vis viva, and increase of vis viva.’” In this manner, the total mass of caloric in a body, called absolute heat, was regarded as a mixture of two components; the free or perceptible caloric could affect a thermometer while the other component, the latent caloric, could not. ^[1] The use of the words “latent heat” implied a similarity to latent heat in the more usual sense; it was regarded as chemically bound to the molecules of the body. In the adiabatic compression of a gas, the absolute heat remained constant by the observed rise of temperature indicated that some latent caloric had become “free” or perceptible. Pierre-Simon Laplace Pierre-Simon Laplace (March 23, 1749 – March 5, 1827) was a French mathematician and astronomer, the discoverer of the Laplace transform and Laplaces equation. ... Antoine-Laurent de Lavoisier (August 26, 1743 - May 8, 1794) was a French nobleman prominent in the histories of chemistry, finance, biology, and economics. ... Vis Viva is the principle that the difference between the aggregate work of the accelerating forces of a system and that of the retarding forces is equal to one half the vis viva accumulated or lost in the system while the work is being done. ...

During the early 19th century, the concept of perceptible or free caloric began to be referred to as “free heat” or heat set free. In 1824, for example, the French physicist Sadi Carnot, in his famous “Reflections on the Motive Power of Fire”, speaks of quantities of heat ‘absorbed or set free’ in different transformations. In 1882, the German physicist and physiologist Hermann von Helmholtz coined the phrase ‘free energy’ for the expression E – TS, in which the change in F (or G) determines the amount of energy ‘free’ for work under the given conditions. ^[2] Sadi Carnot may refer to: Nicolas Léonard Sadi Carnot (1796-1832), French physicist Marie François Sadi Carnot (1837-1894), president of the third French Republic This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ... Hermann von Helmholtz Hermann Ludwig Ferdinand von Helmholtz (August 31, 1821 – September 8, 1894) was a German physician and physicist. ... In thermodynamics, thermodynamic work is a generalisation of the concept of mechanical work in mechanics. ...

In modern use, we attach the term “free” to Gibbs free energy, i.e. for systems at constant pressure and temperature, or to Helmholtz free energy, i.e. for systems at constant volume and temperature, to mean ‘available in the form of useful work.’^[3] With reference to the Gibbs free energy, we add the qualification that it is the energy free for non-volume work.^[4]

To note, some books do not include the attachment “free”, referring to G as simply Gibbs energy. This influence is the result of a 1988 IUPAC meeting designed to unified terminologies between the USA, Europe, and other countries, in which descriptive ‘free’ was supposedly banished.^[5] This ruling, however, is still far from accepted and the majority of published articles and books still use the descriptive ‘free’ for both historical, informative, and for clarification reasons. The International Union of Pure and Applied Chemistry (IUPAC) is an international non-governmental organization devoted to the advancement of chemistry. ...

Useful identities

for constant temperature

and rearranging gives

which relates the electrical potential of a reaction to the equilibrium coefficient for that reaction.

where

ΔG = change in Gibbs energy

ΔH = change in enthalpy

T = absolute temperature

ΔS = change in entropy

R = gas constant

ln = natural logarithm

K = equilibrium constant

Q = reaction quotient

n = number of electrons/mole product

F = Faraday constant (coulombs/mole)

ΔE = electrical potential of the reaction

We also have: Enthalpy (symbolized H, also called heat content) is the sum of the internal energy of matter and the product of its volume multiplied by the pressure. ... [[Image:Translational motion. ... In thermodynamics, entropy, symbolized by S, is a state function of a thermodynamic system defined by the differential quantity , where dQ is the amount of heat absorbed in a reversible process in which the system goes from the one state to another, and T is the absolute temperature. ... The gas constant (also known as the universal or ideal gas constant, usually denoted by symbol R) is a physical constant used in equations of state to relate various groups of state functions to one another. ... The natural logarithm, formerly known as the hyperbolic logarithm, is the logarithm to the base e, where e is equal to 2. ... In chemistry, the equilibrium constant is a quantity characterizing a chemical equilibrium in a chemical reaction which is a useful tool to determine the concentration of various reactants or products in a system where chemical equilibrium occurs. ... In a chemical reaction with certain initial concentrations of reactants and products, it is useful to know if the reaction will shift to the right (increasing the concentrations of the products) or if it will shift to the left (increasing the concentrations of the reactants). ... Properties The electron (also called negatron, commonly represented as e−) is a subatomic particle. ... The mole (symbol: mol) is the SI base unit that measures an amount of substance. ... In physics and chemistry, the Faraday constant is the amount of electric charge of one mole of electrons. ... The coulomb (symbol: C) is the SI unit of electric charge. ... The mole (symbol: mol) is the SI base unit that measures an amount of substance. ... This article is being considered for deletion in accordance with Wikipedias deletion policy. ...

which relates the equilibrium constant with Gibbs energy.

Derivation of

Let S_tot be the total entropy of an isolated system, that is, a system which cannot exchange heat or mass with its surroundings. By the second law of thermodynamics: In thermodynamics, an isolated system, as contrasted with a closed system, is a physical system that does not interact with its surroundings. ... The second law of thermodynamics is a theorem in physics regarding the directional flow of heat in relation to work and which accounts for the phenomenon of irreversibility in thermodynamic systems. ...

and if then the process is reversible.

The heat transfer Q vanishes for an adiabatic system. Any adiabatic process is reversible and isentropic . This article covers adiabatic processes in thermodynamics. ... An isentropic process (a combination of the Greek word iso -same- and entropy) is one during which the entropy of working fluid remains constant. ...

Now consider diabatic systems, having internal entropy S_int. Such a system is thermally connected to its surroundings, which have entropy S_ext.

The entropy form of the second law does not apply directly to the diabatic system, it only applies to the closed system formed by both the system and its surroundings. Therefore a process is possible if

.

We will try to express the left side of this equation entirely in terms of state functions. ΔS_ext is defined as:

Temperature T is the same for two systems in thermal equilibrium. (By the zeroeth law of thermodynamics, if a system is in thermal equilibrium with a second and a third system, the latter two are in equilibrium as well.) Also, Δq_rev is heat transferred to the system, so -Δq_rev is heat transferred to the surroundings, and −ΔQ/T is entropy gained by the surroundings. We now have:

Multiply both sides by T:

ΔQ is heat transferred to the system; if the process is now assumed to be isobaric, then Δq_p = ΔH: An isobaric process is a thermodynamic process in which the pressure stays constant; . The heat transferred to the system does work but also changes the internal energy of the system: according to the first law of thermodynamics, where W is work done by the system, E is internal energy, and...

ΔH is the enthalpy change of reaction (for a chemical reaction at constant pressure and temperature). Then

for a possible process. Let the change ΔG in Gibbs energy be defined as

(1)

Notice that it is not defined in terms of any external state functions, such as ΔS_ext or ΔS_tot. Then the second law becomes:

favored reaction

reversible reaction

disfavored reaction

Also, the sign of Delta G tells us about the spontaneity of the reaction.

Spontaneous

Equilibrium

Nonspontaneous

Gibbs energy G itself is defined as

(2)

but notice that to obtain equation (2) from equation (1) we must assume that T is constant.

Thus, Gibbs energy is most useful for thermochemical processes at constant temperature and pressure: both isothermal and isobaric. Such processes don't move on a P-T diagram, such as phase change of a pure substance, which takes place at the saturation pressure and temperature. However, chemical reactions do undergo changes in chemical potential, which is a state function. Thus, thermodynamic processes are not confined to the two dimensional P-V diagram. There is a third dimension for n, the quantity of gas. Naturally for the study of explosive chemicals, the processes are not necessarily isothermal and isobaric. For these studies, Helmholtz free energy is used. In thermodynamics and chemistry, chemical potential, symbolized by μ, is a term introduced in 1876 by the American mathematical physicist (Willard Gibbs and his partner Lauren Berkley), which he defined as follows: Gibbs noted also that for the purposes of this definition, any chemical element or combination of elements in given... The Helmholtz energy is a thermodynamic potential which measures the useful work obtainable from constant temperature, constant volume thermodynamic systems. ...

Gibbs free energy change of formation

The standard Gibbs free energy of formation of a compound is the change of Gibbs free energy that accompanies the formation of 1 mole of that substance from its component elements, at their standard states (the most stable form of the element at 25 degrees Celsius and 100 kilopascals). Its symbol is ΔG_f^O. The mole (symbol: mol) is the SI base unit that measures an amount of substance. ... In chemistry, the standard state of a material is its state at 1 bar (100 kilopascals) and 25 degrees Celsius (298. ... Celsius is, or relates to, the Celsius temperature scale. ... The pascal (symbol Pa) is the SI unit of pressure. ...

All elements in their standard states (oxygen gas, graphite, etc.) have 0 standard Gibbs free energy change of formation, as there is no change involved. General Name, Symbol, Number oxygen, O, 8 Chemical series Nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless (gas) very pale blue (liquid) Atomic mass 15. ... Graphite (named by Abraham Gottlob Werner in 1789, from the Greek γραφειν: to draw/write, for its use in pencils) is one of the allotropes of carbon. ...

ΔG = ΔG˚ + RTlnK At equilibrium, ΔG=0 so the equation becomes ΔG˚= -RTlnK

Back to Entropy

If a closed system (Δq_rev = 0) is at constant pressure (Δq_rev = ΔH), then

Therefore the Gibbs energy of a closed system is:

and if then this implies that , back to where we started the derivation of ΔG.

See also

• Enthalpy
• Entropy
• Free energy
• Helmholtz free energy
• Thermodynamics
• Willard Gibbs

Enthalpy (symbolized H, also called heat content) is the sum of the internal energy of matter and the product of its volume multiplied by the pressure. ... In thermodynamics, entropy, symbolized by S, is a state function of a thermodynamic system defined by the differential quantity , where dQ is the amount of heat absorbed in a reversible process in which the system goes from the one state to another, and T is the absolute temperature. ... The free energy is a measure of the amount of mechanical (or other) work that can be extracted from a system, and is helpful in engineering applications. ... The Helmholtz energy is a thermodynamic potential which measures the useful work obtainable from constant temperature, constant volume thermodynamic systems. ... Thermodynamics (from the Greek thermos meaning heat and dynamics meaning power) is a branch of physics that studies the effects of changes in temperature, pressure, and volume on physical systems at the macroscopic scale by analyzing the collective motion of their particles using statistics. ... Josiah Willard Gibbs (February 11, 1839 – April 28, 1903) was an American mathematical physicist who contributed much of the theoretical foundation that led to the development of chemical thermodynamics and was one of the founders of vector analysis. ...

References

External links

• Gibbs Free Energy - Eric Weissteins World of Physics
• Gibbs Free Energy - Chemistry Gateway
• Gibbs Free Energy - Illinois State University
• Entropy and Gibbs Free Energy - www.2ndlaw.com
• Gibbs Free Energy - Georgia State University
• Gibbs Free Energy Java Applet - University of California, Berkeley
• Gibbs Free Energy - Florida State University
• IUPAC definition