Computation of complex and constrained equilibria by minimization of the Gibbs free energy

Calculation of chemical equilibria is a good way to determine the composition of a reacting system. This study presents a method for calculating complex equilibria with multiple reactions and phases and adapts it to externally constrained equilibria by introducing energy and kinetic constraints.The proposed method is based on the minimization of the Gibbs free energy, taking into account mass (mole and atom) and charge balances. Examples using different thermodynamic models are presented as well as problems with energy and kinetic constraints. The results are in good agreement with the literature. The calculation method can be applied to a wide variety of fields. Possible extension of the work to electrochemical systems is also addressed.

► Minimization of the Gibbs free energy is applied to constrained equilibria.
► Maximizing entropy is replaced by minimizing Gibbs coupled with an energy balance.
► Adiabatic and non-adiabatic problems can be treated by Gibbs minimization.
► Kinetic constraints allow the evolution of the quasi-equilibrium state with time.