Mean spherical approximation (MSA) for a simple model of electrolytes. I. Theoretical foundations and thermodynamics

A simple electrolyte in a polar solvent is modeled by a mixture of polar hard spheres and equal diameter charged hard spheres. The solution of the mean spherical approximation for this model is rederived to its full extent. Explicit expressions for thermodynamic quantities in terms of the MSA solution are established. A nice property of this MSA approach is the possibility to express quantities of physical interest in terms of a set of three parameters, which represent nothing but the excess internal energies due to charge–charge, charge–dipole, and dipole–dipole interactions, respectively.