In a multicomponent system, where the vapor and liquid consist of more than one type of compounds, describing the equilibrium state is more complicated. For all components  in the system, the equilibrium state between the two phases is described by the following equations:
:; and
where  and  are the temperature and pressure for each phase, and  and are the partial molar Gibbs free energy also called chemical potential (units of energy per amount of substance) within the liquid and vapor, respectively, for each phase. The partial molar Gibbs free energy is defined by:
where  is the (extensive) Gibbs free energy, and  is the amount of substance of component .