A system consists of two phases maintained at constant temperature (T) and pressure (p). The number of moles present in phase 1 and phase 2 of the system is represented by ni (where i = 1, 2) and Gibbs free energy per mole of phase i at this temperature and pressure is gi(T, p). The necessary condition for equilibrium:
1
g1(T, p) > g2(T, p)
2
g1(T, p) = g2(T, p)
3
g1(T, p) < g2(T, p)
4
g1(T, p) = -g2(T, p)