# Gibbs Free Energy

In thermodynamics, the Gibbs free energy (IUPAC recommended name: Gibbs energy or Gibbs function; also known as free enthalpy to distinguish it from Helmholtz free energy) is a thermodynamic potential that measures the "useful" or process-initiating work obtainable from a thermodynamic system at a constant temperature and pressure (isothermal, isobaric). Just as in mechanics, where potential energy is defined as capacity to do work, similarly different potentials have different meanings. The Gibbs free energy is the maximum amount of non-expansion work that can be extracted from a closed system; this maximum can be attained only in a completely reversible process. When a system changes from a well-defined initial state to a well-defined final state, the Gibbs free energy ΔG equals the work exchanged by the system with its surroundings, minus the work of the pressure forces, during a reversible transformation of the system from the same initial state to the same final state.

Gibbs energy (also referred to as ∆G) is also the chemical potential that is minimized when a system reaches equilibrium at constant pressure and temperature. Its derivative with respect to the reaction coordinate of the system vanishes at the equilibrium point. As such, it is a convenient criterion of spontaneity for processes with constant pressure and temperature.

The Gibbs free energy, originally called available energy, was developed in the 1870s by the American mathematician Josiah Willard Gibbs. In 1873, Gibbs described this “available energy” as

the greatest amount of mechanical work which can be obtained from a given quantity of a certain substance in a given initial state, without increasing its total volume or allowing heat to pass to or from external bodies, except such as at the close of the processes are left in their initial condition.

The initial state of the body, according to Gibbs, is supposed to be such that "the body can be made to pass from it to states of dissipated energy by reversible processes." In his 1876 magnum opus On the Equilibrium of Heterogeneous Substances, a graphical analysis of multi-phase chemical systems, he engaged his thoughts on chemical free energy in full.

Read more about Gibbs Free Energy:  Overview, History, Graphical Interpretation, Definitions, Derivation, Free Energy of Reactions, Useful Identities, Standard Energy Change of Formation

### Other articles related to "gibbs free energy, energy, gibbs":

Saturated Fluid - Thermodynamic Description of Vapor–liquid Equilibrium - Multicomponent Systems
... for each phase, and and are the partial molar Gibbs free energy also called chemical potential (units of energy per amount of substance) within the liquid and vapor, respectively, for each phase ... The partial molar Gibbs free energy is defined by where G is the (extensive) Gibbs free energy, and ni is the amount of substance of component i ...
Glossary Of Fuel Cell Terms - G - Gibbs Free Energy
... In thermodynamics, the Gibbs free energy (IUPAC recommended name Gibbs energy or Gibbs function) is a thermodynamic potential which measures the "use ...
Exergonic Reaction
... chemical reaction where the change in the Gibbs free energy is negative, indicating a spontaneous reaction ... Symbolically, the release of Gibbs free energy, G, in an exergonic reaction is denoted as Although exergonic reactions are said to occur spontaneously, this ... More generally, the terms exergonic and endergonic relate to the Gibbs free energy change in any process, not just chemical reactions ...
Gibbs Isotherm - The Gibbs Adsorption Isotherm Equation - Derivation of The Gibbs Adsorption Equation
... β phase in equilibrium with a surface s dividing the phases, the total Gibbs free energy of a system can be written as where G is the Gibbs free energy ... The equation of the Gibbs Adsorption Isotherm can be derived from the “particularization to the thermodynamics of the Euler theorem on homogeneous first-order forms.” The Gibbs free energy of each phase ... By taking the total derivative of the Euler form of the Gibbs equation for the α phase, β phase and the surface phase where A is the cross sectional area of the dividing surface, and γ is the ...

### Famous quotes containing the words energy and/or free:

Three elements go to make up an idea. The first is its intrinsic quality as a feeling. The second is the energy with which it affects other ideas, an energy which is infinite in the here-and-nowness of immediate sensation, finite and relative in the recency of the past. The third element is the tendency of an idea to bring along other ideas with it.
Charles Sanders Peirce (1839–1914)

No man hath any quarrel to me. My remembrance is very free and clear from any image of offence done to any man.
William Shakespeare (1564–1616)