The heat capacity of the adsorbate adsorbent system is a crucial physical property required for modeling adsorption cycles. It is specific to the considered adsorptive gas and to the corresponding adsorbent. In previous work, it has been shown that this heat capacity can be estimated using only the properties of the gaseous phase, the adsorption equilibria, and the isosteric heats of adsorption. As these quantities are required in any case for simulations, no additional effort arises. In this paper, the separated adsorbed phase heat capacities are computed at higher accuracies by employing reversible thermodynamic paths, which traverse equilibrium states only. As a result, the thermodynamic consistency of the model improves, since the residuals of the energy and entropy balances are significantly smaller. Results are given for the water-zeolite 13X adsorption pair.