Computation of phase and chemical equilibrium: Part I. Local and constrained minima in Gibbs free energy

Several methods are reviewed for determining compositions in multiphase, reacting mixtures at equilibrium. Wolfe's quadratic programming algorithm is applied and results compared with the Rand method (Dluzniewski and Adler 1972), NASA method (Gordon and McBride 1971) and the George et al. (1976) implementation of Powell's method. For poor guesses in compositions, local and constrained minima in Gibbs free energy may arise, giving incorrect phase distributions.