Generalization of the Maxwell Criterion for Van der Waals Equation

Abstract

A method is proposed for generalizing the Maxwell equal-area rule for replacing isobaric isotherm segments in the condensing phase for van der Waals equation. The new vapor-pressure isotherm cuts off lobes unequal by an amount depending on the internal energies and differing specific heats of the liquid and vapor phases. Improved predictions of both liquid specific heat and entropy of vaporization for some metals are demonstrated by a simple example.