Analytical equation of state for molecular fluids: Comparison with experimental data

Abstract

An analytical equation of state for real molecular fluids is presented, based on an extension of a previously presented perturbation theory for hard convex bodies [Song and Mason, preceding paper, Phys. Rev. A 42, xxxx (1990)]. It is a fifth-order polynomial in the density and seems to be valid over the range from the dilute gas to the metastable liquid, both below and above the critical temperature. The temperature-dependent parameters of the equation can be calculated if the intermolecular pair potential is known. However, knowledge of just the second virial coefficient plus some liquid densities is sufficient to predict reasonably accurate parameters and hence the whole p-v-T surface. Three scaling constants characterize the equation: an interaction energy, an interaction distance, and a dimensionless nonsphericity or inner hard-core parameter. The equation is tested with experimental p-v-T data for eight selected systems: ${\mathrm{N}}_2$, ${\mathrm{CO}}_2$, ${\mathrm{C}}_2$ ${\mathrm{H}}_6$, ${\mathrm{C}}_3$ ${\mathrm{H}}_8$, ${\mathrm{CF}}_4$, ${\mathrm{SF}}_6$, ${\mathrm{NH}}_3$, and ${\mathrm{H}}_2$O. Agreement is quite remarkable.