This review aims to be self-contained and thus we begin with a brief overview of the relevant thermochemical properties and relationships. When working with thermochemical data related to heterogeneous catalysis or any other system, it is imperative to recognize that any thermochemically meaningful quantity will be a relative quantity that satisfies a mass balance. Here, we focus on chemical processes occurring at a fixed temperature and pressure; hence, we use Gibbs free energy ∆G as the relevant thermochemical potential. Thermodynamic equilibrium governs the maximum achievable conversion and selectivity for a chemical conversion process. The equilibrium constant K for a reaction is calculated from the Gibbs free energy change ∆ r G at a temperature T