Statistical Mechanics of Condensing Systems. III

A general development of the Gibbs phase integral for a system of chemically saturated molecules gives equations for the thermodynamic properties of the system. The equations predict the usual condensation phenomenon of the gas to form a condensed phase with a surface tension at temperatures below a characteristic temperature Tm. At Tm the surface tension of the condensed phase is zero, and this phase undergoes a discontinuous change without heat of transition. Between Tm and the true critical temperature Tc, there exists a finite volume interval for which P and the Gibbs free energy F is independent of the volume. Above Tc the usual P—V diagram predicted above the critical point is found, with no volume for which (∂P/∂V)T is zero.