Thermodynamics of 3-Phase Equilibrium in Argon Based on a Perfect Solid and Liquid

Three-phase equilibrium in argon was obtained based on the thermodynamics of a perfect solid and liquid. The equation of state (EOS) for a perfect solid was previously obtained from the study of a pure substance with spherical molecules. The EOS for a perfect liquid is a van der Waals EOS with suitable coefficients to explain 3-phase equilibrium. The Lennard-Jones parameters for argon are applied to these EOSs. Thep-V-Trelations on the equilibrium lines are comparable with experimental and molecular simulation results. The calculated values of the average potential energy and entropy are also consistent with the simulations.