Chemical equilibrium can be calculated either stoichiometrically or non-stoichiometrically: The stoichiometric approach (SM) involves calculating the equilibrium constants of a set of independent reactions and determining the equilibrium composition from a specified initial composition and the equilibrium extents of the specified reactions. In the non-stoichiometric approach, commonly referred to as Gibbs energy minimization (GEM) approach, the equilibrium composition is determined by finding the one distribution of the initially available atoms between the specified reactant and product molecules that has the minimum overall Gibbs energy. Note that essentially, both approaches are forms of minimization of the Gibbs energy as shown by Smith et al. , but GEM in this work refers to the non-stoichiometric approach.