Thermodynamic Properties of Gaseous Argon from the Ab Initio Virial Equation of State

A previously developed ab initio virial equation of state for argon (B. Jäger, R. Hellmann, E. Bich, E. Vogel, J. Chem. Phys. 135 (2011) 084308) was applied to calculate related thermophysical properties for the gaseous and supercritical region. Virial coefficients up to B 7 were included considering also nonadditive three-body interactions and quantum corrections (for B 2, B 3, and B 4). The results for the isothermal compressibility, the thermal expansivity, the isochoric and isobaric heat capacity, and for the speed of sound were compared with experimental data and with values obtained from a highly accurate empirical equation of state. It was generally found that the theoretical predictions are in very good agreement with the reference data except for the near-critical region and for higher densities. Hence, the theoretically calculated data can be useful for the improvement of equations of state, particularly for toxic or corrosive substances and for thermodynamic conditions, where experiments are difficult to perform (e.g. at high temperatures). The speed of sound was found to be the most suitable property to evaluate the quality of the underlying interaction potentials.