Surface Equilibria

This chapter starts by giving a brief review of the theory of chemical equilibria. It then extends those concepts to describe surface reactions. The key thermodynamic concept for describing equilibria in chemical processes is the Gibbs free energy, which plays a role in chemistry. In order to determine the change in free energy, ΔG, of an adsorption process, there is a need to know both the adsorption energy and the adsorption entropy. The chapter first discusses adsorption energy, and then discusses the gas-phase and adsorption-phase entropy. It examines how the equilibrium surface coverages depend on the adsorption strength of the adsorbing molecule and the influence of temperature and pressure. The Gibbs free energy diagrams take the effects of temperature and pressure into account by showing the “configurationally corrected Gibbs free energy levels” of every reaction step with respect to the reactants.