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.