This paper sets optimal control framework for balance and kinetic equations of multiphase reacting systems consistently with the second law of thermodynamics. Approaches effective in contemporary theory of nonequilibrium thermodynamics of single-phase systems are here extended to include interfacial discontinuities, surface reactions and interface transports which are phenomena typical of multiphase systems. We arrive at Lagrangian and Hamiltonian structures of transport equations and laws of chemical kinetics, which constitute efficient forms serving to generalize linear models to nonlinear regimes. Local disequilibria are predicted which are shown to be responsible for onset of interfacial and bulk instabilities.