Heat capacities of weak electrolytes and ion association reactions: method and application to aqueous MgSO4 and HIO3 at 298 K

Abstract

Analysis of heat capacities for weak electrolytes (or 'almost strong' electrolytes) in terms of the various solute species is shown to require allowance for the thermal effects associated with the shift of the association or dissociation equilibrium when the temperature changes during a calorimetric measurement. This shift of equilibrium state is related to changes in the equilibrium constant and activity coefficient with temperature, as expressed by thermodynamic equations we have derived. These equations have been applied to aqueous MgSO4 and HIO3 to obtain the contributions of the solute species to the apparent molal heat capacities, which are then analyzed to yield heat capacities of MgSO4 (aq, undiss.) and HIO3 (aq, undiss.) and ΔCP0 values for the association reactions of the ions to form these species.