Abstract In this paper, the effects of an inert carrier gas and steam flow on the reaction kinetics of a CuCl2 hydrolysis reactor are examined for the thermochemical copper-chlorine (Cu–Cl) cycle of hydrogen production. Experimental data from two packed bed reactors, at three separate vapour pressures of H2O in the gaseous input stream, are investigated in terms of the transient conversion efficiencies and reaction kinetics. The results show that the transient reaction rate reduces by over 75% as the reaction progresses and physical resistances develop in the reactor. The effects of system temperature and reactant flowrate on the reaction rate are also investigated with experimental data. The results of this paper show that by reducing the steam density, the variability in reaction rate can be decreased. These results can be used to predict the reaction kinetics, allowing residence time and transport properties to be more effectively considered.