GIBBS FREE ENERGY

(G) A thermodynamic property devised by Josiah Willard Gibbs in 1876 to predict whether a process will occur spontaneously at constant pressure and temperature. Gibbs free energy G is defined as G = H - TS where H , T and S are the enthalpy , temperature , and entropy . Changes in G correspond to changes in free energy for processes occuring at constant temperature and pressure; the Gibbs free energy change corresponds to the maximum nonexpansion work that can be obtained under these conditions. The sign of Delta G is negative for all spontaneous processes and zero for processes at equilibrium .