Endothermic or exothermic character of the dissociation of ion pairs

Abstract

In the gaseous phase the dissociation enthalpy AHd of ion pairs is always positive. In the liquid phase the polarization of the molecules of the medium around the separate ions decreases the dissociation enthalpy and in some cases renders it negative. Other factors which influence the enthalpy of dissociation are the formation of hydropen bonds or charge transfer bonds between the ions o r between the ions and the solvent molecules. An equation based on the theories of Denison and Ramsey and o f Gilkerson which takes these effects into account is : AHd = (eZN/aD) (confronted with the data of the literature.