Gibbs free energy

A thermodynamic potential defined as enthalpy minus temperature times entropy. At constant temperature and pressure, its change indicates whether a process is thermodynamically spontaneous.

Gibbs energy change: The difference in Gibbs free energy between a process’s final and initial states. A negative change indicates thermodynamic spontaneity under constant-temperature, constant-pressure conditions.
Enthalpy: A thermodynamic state function equal to internal energy plus pressure times volume. Enthalpy supplies the energy contribution in the definition of Gibbs free energy.
Gibbs free energy of formation: The Gibbs free energy change for forming one mole of a substance from its elements in standard states. Formation values let chemists calculate reaction free-energy changes from tabulated data.
Helmholtz free energy: A thermodynamic potential equal to internal energy minus temperature times entropy. It is the corresponding spontaneity criterion at constant temperature and volume.
Chemical potential: The change in a system’s thermodynamic potential when the amount of a substance changes. Chemical potential expresses how Gibbs free energy responds to changes in composition.
Entropy: A thermodynamic state function measuring energy dispersal and the number of accessible microscopic arrangements. The entropy term explains why increased disorder can favor processes despite their enthalpy cost.
Electrochemical cell: A device in which redox reactions convert chemical energy into electrical energy or the reverse. The free-energy change of its reaction determines the maximum electrical work and cell voltage.
Internal energy: The total microscopic kinetic and potential energy contained within a thermodynamic system. Unlike Gibbs free energy, it is the natural potential for isolated systems at fixed volume and entropy.
Chemical equilibrium: A state in which forward and reverse chemical reactions proceed at equal rates. At equilibrium, Gibbs free energy is minimized for the system’s constraints.
Temperature: A physical quantity that determines the direction of heat flow between systems in thermal contact. Temperature weights the entropy contribution in the Gibbs free energy expression.

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