PHASE DIAGRAM AND PV ISOTHERMS OF ARGON

A simple model for classical fluids has been applied to argon. The model contains only the excess entropy of hard spheres and the second virial coefficient for the actual intermolecular potential function. Three forms of the potential were used in the computation. Thermodynamic functions in one-phase regions and the location of the gas-liquid transition were calculated. Insensitivity to the potential shape was found over a large region in density and temperature. A simple extension of the model was used to estimate the location of the fluid-solid transition. The agreement with experiment is very good for the phase diagram in the pressure-temperature plane and moderate for the coexisting densities. Calculated and experimental pressures, entropies, and internal energies are compared in the fluid region.