This paper examines cupric chloride solid conversion during hydrolysis in the thermochemical copper-chlorine (Cu-Cl) cycle of hydrogen production. The hydrolysis reaction is a challenging step, due to the excess steam requirement and decomposition of cupric chloride (CuCl(2)) into cuprous chloride (CuCl) and chlorine (Cl(2)). In this paper, the hydrolysis and decomposition reactions are analyzed with respect to chemical equilibrium conversion and the reaction kinetics. The effects of operating parameters are examined, including the temperature, pressure and excess steam, on equilibrium conversion. It is shown that the reaction kinetics expression that represents a reversible reaction reflects the equilibrium limitation on the solid conversion, rather than first-order kinetics. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.