Coexistence curve of monodisperse gases

Abstract

We present and discuss two equations of state for monodisperse systems. The first one is a general, semi-empiric, cubic equation of state written in terms of three constant parameters and a temperature dependent function for which the second virial coefficient may be used to obtain an analytically manipulable expression. The second equation is obtained by means of the mean spherical approximation (MSA) and depends on two parameters, one for the range, and the other for the amplitude, of the interaction potential. The aim of this paper is to present the mathematical and numerical techniques used to obtain the coexistence curve of monodisperse gases. This is made for the two equations of state and the corresponding appropriate methods to obtain the coexistence curve: Maxwell's equal-area rule, for the cubic equation, and the equilibrium condition of the chemical potential of the coexisting phases, for the MSA result. We compare our results with recently reported experimental data for Ar. With this work, we intend to acquaint the reader with both equations and their application possibilities, and also with the mathematical and computational tools required to find the coexistence curves.