Solubility product— solvent activity coefficients from

Any consideration of sovent effects on rates or equilibria must start from solvent activity coefficients, VI for reactants, transition states and products (Wiberg, 1964 Laidler, 1950 Parker, 1966). Once solvent activity coefficients are available, or can be predicted, it is highly probable, as indicated at the end of this article, that an enormous amoimt of information on the kinetics of reactions in solution and on equilibrium properties such as solubility, acid-base strength, ion-association, complexing, redox potentials and kinetics of reactions in different solvents (Parker, 1962, 1965a, 1966) can be reduced to a relatively small number of constants which can then be used in appropriate linear free energy relationships. 

In solvents that are chemically similar to the solute (i.e., naphthalene/toluene), the experimental solubility of the solute is very close to the ideal value. Either negative or positive deviation from the ideal value occurs when the solute and the solvent are chemically dissimilar. The nonideal behavior results from the differences in the interactions between the solute and the solvent molecules (i.e., solute-solute, solvent-solvent, and solute-solvent). The sum of these interactions usually becomes positive, and having an incomplete mixing of all components results in a finite solubility of the solute in the solvent. These deviations from ideal solution behavior can be expressed by the activity coefficient of the nonideal solution. The activity, a2, of a solute in a nonideal solution is the product of concentration, x2, and the activity coefficient, y2, as ... 

The solubility product quotient at 25 C (pA Mncos = 11.09, pAT acoj = 8.37) can now be compart with an experimental value of D. The data of Bodine et al. (1965) give = 17.4 (25 C). Because D is smaller than the ratio of the K q values, the solid solution factor acts to lower the solution of MnC03 in CaCOs significantly from that expected if an ideal mixture has been formed. If it is assumed that in dilute solid dilutions (Xm co3 very small) the activity coefficient of the solvent is close to unity fc coj — 1) an... 

---