We have studied the first two terms of the high-temperature equation of state, p/ρkT = a(ρ) + b(ρ)/kT + c/(kT)2 + ..., of a simple spherical fluid whose intermolecular potential is the sum of a hard core and soft (mostly attractive) contribution. a(ρ) and b(ρ) are known functionals of the pressure and radial distribution function of a fluid whose potential is solely composed of the hard-core contribution. Approximate expressions for a(ρ) are obtained by using the hard-sphere equation of state and radial distribution function of the approximate Percus-Yevick theory. We show that b(ρ) can be expressed directly as a quadrature of the Laplace transform of the approximate radial distribution function (which is explicitly known); no inversion of the transform is necessary. Choosing for the soft potential a truncated Lennard-Jones potential, we compare the resulting first two terms of the series with experimental data for argon for densities between 40 and 600 amagats and temperatures from 0 to 150°. The intercept a(ρ) is in good agreement with that theoretically computed. The theory can reproduce the b(ρ), found from experiment, if the parameters of the truncated Lennard-Jones potential are varied by about 5%.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry