A GENERAL MIXTURE THEORY .1. MIXTURES OF SPHERICAL MOLECULES

We present a new general theory for obtaining mixture properties from the pure species equations of state. The theory addresses the composit ion and the unlike interactions dependence of mixture equation of stat e. The density expansion of the mixture equation gives the exact compo sition dependence of all virial coefficients. The theory introduces mu ltiple-index parameters that can be calculated from binary unlike inte raction parameters. In this first part of the work, details are presen ted for the first and second levels of approximations for spherical mo lecules. The second order model is simple and very accurate. It predic ts the compressibility factor of additive hard spheres within simulati on uncertainty (equimolar with size ratio of three). For nonadditive h ard spheres, comparison with compressibility factor simulation data ov er a wide range of density, composition, and nonadditivity parameter, gave an average error of 2%. For mixtures of Lennard-Jones molecules, the model predictions are better than the Weeks-Chandler-Anderson pert urbation theory. (C) 1996 American Institute of Physics.