Intermolecular Potential Functions and the Second and Third Virial Coefficients

Abstract

Potential parameters are determined from second virial coefficient data for the Lennard‐Jones, Kihara, square‐well, exp‐6, and Sutherland potentials. Using these parameters, third virial coefficients are calculated from theoretical tabulations and compared with experimental values. Substances considered are: Ar, N₂, Kr, CH₄, CO₂, Xe, CF₄, n‐pentane, neopentane, and benzene. For the exp‐6 potential, theoretical second virial coefficients are tabulated for the additional third parameter values necessary to represent the experimental data. Each of the three‐parameter models, including the square‐well, fit the second virial coefficient data within experimental accuracy, and considerably better than the two‐parameter potentials. Calculated third virial coefficients form a characteristic family of curves for the various potential models. The contribution of nonadditive attractive forces to the third virial coefficient is significant, especially at low temperatures. The three‐parameter potentials give reasonable agreement with experiment but no single potential is outstanding, possibly due to the neglect of nonadditive repulsive forces.