High-Temperature Equation of State by a Perturbation Method. I. Nonpolar Gases

TLDR

The authors develop a perturbation theory that relates the thermodynamic properties of high‑temperature argon and nitrogen to a rigid‑sphere fluid, using a Lennard‑Jones potential with an adjustable cutoff as the perturbation. The resulting equations of state agree fairly well with experimental data and provide a basis for experimentally testing the rigid‑sphere model.

Abstract

A theoretical study is made of the equations of state of argon and nitrogen, at high temperatures and densities. The intermolecular potential used is of the Lennard-Jones form, with an adjustable rigid sphere cutoff. A perturbation theory is developed, by which the thermodynamic properties of one system may be related to those of a slightly different system and to the difference in the intermolecular potentials of the two systems. In this article, the unperturbed system is a rigid sphere fluid, and the Lennard-Jones potential is the perturbation. The results are in fair agreement with experiment, and also lead to an experimental test of the theoretical rigid sphere equation of state.