### Gibbs Free Energy Definition

Gibbs free energy is a measure of the potential for reversible or maximum work that may be done by a system at constant temperature and pressure. It is a thermodynamic property that was defined in 1876 by Josiah Willard Gibbs to predict whether a process will occur spontaneously at constant temperature and pressure. Gibbs free energy G is defined as G = H - TS where H, T and S are the enthalpy, temperature, and entropy.

The SI unit for Gibbs energy is the kilojoule (kJ).

Changes in the Gibbs free energy G correspond to changes in free energy for processes at constant temperature and pressure. The change in Gibbs free energy change is the maximum nonexpansion work obtainable under these conditions in a closed system. ΔG is negative for spontaneous processes, positive for nonspontaneous processes and zero for processes at equilibrium.

**Also Known As: **(G), Gibbs' free energy, Gibbs energy, or Gibbs function. Sometimes the term "free enthalpy" is used to distinguish it from Helmholtz free energy.

The terminology recommended by the IUPAC is Gibbs energy or Gibbs function.