Thermodynamics of complex dissociation in aqueous solution at elevated temperatures

Abstract

The temperature dependence of the thermodynamics of dissociation for complexes in the temperature range 0-370° is described in terms of functions involving the dielectric constant of water and a power series consistent with nonelectrostatic interaction in the absence of a dielectric medium. Evaluation of the theoretical equations for various reactions yields results in close agreement with published thermodynamic data. Heat capacities of dissociation may vary monotonously with temperature or pass through extrema depending on the relative influence of electrostatic and nonelectrostatic interaction on the stabilities of the complexes as temperature increases. When the dielectric constant of the solvent becomes small at high temperatures, the electrostatic contribution dominates. As a consequence, many complexes become significantly stable at high temperatures, and the enthalpies, entropies, and heat capacities of dissociation become relatively large negative numbers.