This paper documents an analytical and numerical study of thermochemical energy storage in an open reactor. The analysis of the pressure losses and temperature distributions allows to predict what the geometrical features of the reactor should be. A numerical model simulating the thermochemical process is then presented and validated. In accord with the Constructal design methodology, the module configuration is morphed following the trends obtained in the analytical part, to head for better overall performances. The results show that the ratio between the heat produced by the chemical reaction within the entire module and the overall pumping power necessary to blow the fluid through the module increases as the imperfections reach equipartition. In terms of module configuration, this means (i) an increase in the number of salt layers and (ii) aspect ratios moving the module volume towards more compactness.