|MadSci Network: Chemistry|
Thermodynamic equilibrium expressions are based on the activity of the reactants and products. We commonly use concentrations when we deal with dilute (ideal) solutions. Activity is the concentration times the acitvity coeffient of the compound. For solids, the activity is defined as 1. Increasing the surface area will certainly increase the rate of the forward reaction, but it will also increase the rate of the backward reaction since now there are more speicies in that have reacted with the solids. The net result is compliance with Le Chatelier's law.
Try the links in the MadSci Library for more information on Chemistry.