Statistical thermodynamics of solutions of molecules with spherical field of forces

The cell model for solutions, used by one of the authors (I. P.) and his collaborators, is extended to mixtures of spherical molecules of slightly different radii. To take account of this difference, we introduce two characteristic distances aA and aB, which are the mean distances of the first neighbours of a molecule A and of a molecule B. These distances are fixed by a condition of minimum free energy. The thermodynamic excess functions for the solution (excess free energy, energy, entropy and volume) are expressed in terms of purely molecular data.