Thermochemical materials, particularly salt hydrates, have significant potential for use in thermal energy storage applications. When a salt hydrate is heated to a threshold temperature, a chemical reaction is initiated to dissociate it into its anhydrous form and water vapor. The anhydrous salt stores the sensible energy that was supplied for dehydration, which can be later extracted by allowing cooler water or water vapor to flow through the salt, transforming the stored energy into sensible heat. We model the heat release that occurs during a thermochemical hydration reaction using relations for mass and energy conservation, and for chemical kinetics and stoichiometry. A set of physically significant dimensionless parameters reduces the number of design variables. Through a robust sensitivity analysis, we identify those parameters from this group that more significantly influence the performance of the heat release process, namely a modified Damkohler number, the thermochemical heat capacity, and the heat flux and flowrate. There is a strong nonlinear relationship between these parameters and the process efficiency. The optimization of the efficiency with respect to the parameters provides guidance for designing engineering solutions in terms of material selection and system properties. (C) 2011 Elsevier Ltd. All rights reserved.