Activity Coefficients of an Electrolyte in a Mixture with a High Density Neutral Component

Abstract

Activity coefficients for the primitive model electrolyte, containing a high concentration of neutral hard spheres, are calculated for the modified Poisson−Boltzmann (MPB), hypernetted chain (HNC), and mean spherical approximation (MSA) theories. Comparisons are made with Monte Carlo (MC) simulation results for a 1:1 electrolyte having a common ion diameter with the neutral molecule diameter equal or different to that of the ions. Various electrolyte concentrations are treated with the overall packing fraction held fixed at 0.3. A very good agreement with simulation for the MPB theory is found for the charging parameter approach, that via the virial route being less accurate. The MSA activity coefficients via the energy route also give a good representation of the simulation values, while the HNC theory is adequate only for low volume fractions of added neutral particles.