LINEAR FREE-ENERGY RELATIONS FOR PREDICTING DISSOLUTION RATES OF SOLIDS

A QUANTITATIVE understanding of the rates and mechanisms of dissolution Of crystalline solids in aqueous solutions is critical to the chemical modelling of many geochemical, environmental and industrial processes. Here I show that a linear free energy equation, developed recently1,2 for the prediction of the standard Gibbs free energies of formation of isostructural families of crystalline solids, can also be used for predicting the dissolution rates of solids. This equation bears a close analogy with the Hammett equation for aqueous organics3. Regression of data for the surface-reaction-controlled dissolution rates of isostructural families of divalent metal oxides and orthosilicates using the new equation yields coefficients characteristic of the specific crystal structure, which turn out to be very close to the coefficients obtained by regression of standard free energy data for the same families. The results suggest that standard free energy coefficients can be used to predict dissolution rates.