Physical adequacy of parameters in statistical-mechanical calculations of the properties of strong electrolyte solutions

Abstract

Calculations have been carried out on the distribution functions, free energy ΔF, and heats of dilution ΔH for a 1-1 electrolyte solution with a variety of parameters representative of noncoulombic short-range interionic interaction in water at 15–40°C using a theoretical equation which is strictly valid at c<0.1 moles-liter⁻¹ and gives a good approximation up to c=0.3. The main result is that agreement with experimental ΔH data could be obtained by very small, physically highly reasonable variations of the interionic specific potentialU _ab(r) of the order of 1% per degree centigrade. Any change in the distance of specific interactionr _c gives an appreciable contribution to ΔH only if it is taken in the form of its temperature derivative. These contributions are large enough to account for the experimental data if one takes simultaneously into account appropriate changes ofU _ab(r) nearr _c to conjugate the former smoothly with the coulomb potential atr=r _c. To fit the calculated ΔH to experimental data for NaCl in H₂O at 25°C it is necessary to allow the solvation of ions to increase with increasing temperature, which is in agreement with experiment.