The Phase Rule and Heterogeneous Equilibria

Abstract

The phase rule relates the observed state of the heterogeneous system with number of thermodynamic variables required for the energetic description of its state as equilibrium. The phase rule is stated simply as the mnemonic, Φ = C − P + 2, where Φ is the variance = number of state variables that must be independently fixed or determined, C is the number of components, and P is the number of phases observed. The factor of 2 arises from the normal number of intensive variables, temperature and pressure.