Evaluating the integral expression for g ( p , T ) given previously between the saturated liquid and vapor states and applying the Gibbs criterion of material equilibrium to this phase change process requires writing it as g g − − g f = ∫ ∫ p s p m i n v l d p + ∫ ∫ p m i n p m a x v u d p + ∫ ∫ p m a x p s v v d p = 0