In this paper, a multiphase reacting system with thermal decomposition of solid reactant particles and phase transition of a molten product at a gas-liquid-solid interface are analyzed. A new predictive model is developed for the mass and heat transfer, as well as the reaction kinetics. The predicted results fit well with experimental data. The analysis is applied to the decomposition of solid particles of CuO-CuCl2 (copper oxychloride) in a molten salt environment of the thermo-chemical copper-chlorine (Cu-Cl) cycle of hydrogen generation. Oxygen gas is released from the thermal decomposition of copper oxychloride particles. This reaction establishes the high temperature limit of the thermo-chemical cycle at 530 degrees C. A Stefan boundary condition is used to track the position of the moving solid-liquid interface as the solid particle decomposes to produce molten product under the input of a heat flux at the surface. The results of conversion of CuO-CuCl2 from both a thermo-gravimetric (TGA) microbalance and large laboratory scale batch reactor experiments are analyzed and the rate of endothermic reaction is measured to determine the heat transfer rate. The resulting reaction rate is incorporated into the model, and the controlling resistances are analyzed. The predicted results are successfully compared and validated against experimental data. (C) 2012 Elsevier Ltd. All rights reserved.