Abstract
The thermodynamics of solution of nonelectrolytes in a number of solvents have been studied theoretically and experimentally. The validity of the two more important theories of solution, i.e. scaled-particle theory (SPT) and Sinanoglu-Reisse-Moura-Ramos theory (SRMR), which have been put forward to account for the solubility of gases and vapours have been investigated. It is shown that neither theory can be used to predict accurately the solubilities of gases and vapours, especially in nonaqueous solvents. Heats of solution of a large, spherical, nonpolar molecule, Me[4]Sn(liquid), have been measured calorimetrically and combined with the known heat of vaporisation to obtain heats of solution of Me[4]Sn(gas) in nonaqueous solvents. Gas chromatographic head space analysis has been used to obtain Raoult's law activity coefficients of Me4Sn in nonaqueous solvents,and thence to obtain DeltaG°[s] , DeltaH°[s] and DeltaS°[s] for solution of Me[4]Sn(gas). The observed values of these quantities have been compared with those calculated by SPT and SRMR theory, and it is shown that neither theory yields values in agreement with experiment. The Menschutkin reaction has been studied kinetically in several solvents at different temperatures, and the activation parameters calculated. Heats of solution of the reactants have been determined and combined with known free energies of solution to yield entropies of solution. Combination with the corresponding activation parameters enables the solvent effect on the transition-state to be determined in terms of G, and S. It is shown that transition-state effects are greater than initial-state effects. Similar experiments have been carried out for the unimolecular reactions of t-butyl halides and it is shown again that in nonaqueous solvents, the solvent effects on the reactants are generally quite small.