Molecular theory of the volume change accompanying contact-complex formation reactions in solution

Abstract

A theoretical expression of the volume change accompanying the contact‐complex formation in the hard‐sphere fluid at infinite dilution has been derived by using the radial distribution function and the equation of state. It is revealed that the volume change is composed of the two additive terms related to (i) the molecular packing and (ii) the thermal motion of molecules. In order to comprehend the volume change at the molecular level, the numerical calculation of the volume change based on the theory developed has been performed as a function of the solvent density and the size ratio of the solute to the solvent molecules. The volume changes obtained at liquid densities are dominated by the molecular packing term, and their values in solvents of the common size are in the range of −5 to −10 cm3 mol− 1 in reasonable agreement with the experimental results for the weak EDA complexes in solution.