SOLVENT MEAN FORCE PERTURBATIONS OF DIATOMIC DISSOCIATION REACTIONS -COMPARISON OF PERTURBED HARD FLUID AND COMPUTER-SIMULATION RESULTS

The perturbed hard fluid model, which separates solute-solvent interac tions into repulsive hard sphere and mean field attractive contributio ns, is applied to predict solvent effects on the thermodynamics of dia tomic dissociation reactions. Theoretically predicted changes in exces s Gibbs free energy (Delta G), entropy (Delta S), enthalpy (Delta H), and volume (Delta V) for the dissociation of a homonuclear diatomic di ssolved in a monatomic solvent, with Lennard-Jones solute atom-solvent atom and solvent-solvent interaction potentials, are compared with co mputer simulation results. The perturbed hard fluid model requires onl y one adjustable parameter, which is determined using simulation resul ts at a single temperature and density. This parameter is used in the prediction of reaction thermodynamics over the entire vapor, liquid, a nd supercritical fluid regime. Furthermore, the thermodynamics of othe r reactions, in which the solute atom-solvent atom attractive well dep th changes upon dissociation, can be predicted by including one additi onal parameter, determined using only simulation results for a system with no well depth change.