SOLVENT REORGANIZATION AND THERMODYNAMIC ENTHALPY-ENTROPY COMPENSATION

This paper develops a formalism for treating the solvent reorganizatio n that accompanies all chemical reactions and physical processes in li quid solutions, In particular, cage environments are shown explicitly, and overall equations are separated ito a nominal equation (which is essentially the conventional chemical equation) and an environmental ( env) equation. The separation is useful because it follows from the Se cond Law that in dilute solution Delta G(env) (same as Delta G degrees (env)) for solvent reorganization is generally zero, so that the nomin al equation accounts for the observed standard free energy change Delt a G degrees associated with the process. On the other hand, Delta H-en v and Delta S-env can be substantial, especially when the solvation in volves hydrogen bonding. And since Delta G(env) = 0, there is enthalpy -entropy compensation to the extent that Delta H-env = T Delta S-env. Conventional thermodynamic accounting requires that Delta H-env and De lta S-env are added to, and become part of, Delta H degrees and Delta S degrees for the overall process. Thus, when Delta H-env >> Delta G d egrees, the plot of Delta H degrees vs Delta S degrees is nearly a str aight line, with a slope close to the experimental temperature T. Two examples approaching this situation are presented and discussed.