Adsorption isosteric heat (Qiso) can be determined both by differential calorimetry or by two isotherms (Clausius-Clapeyron). From Qiso the differential molar entropy of the adsorbed phase could be calculated by Sa= Sg -Qiso/T where Sg is the integral molar entropy of the gas. Finally, the specific heat could be obtained by Cp= T(dSa/dT), but the question is: the specific heat so calculated represents only the internal energy change due to adsorption, or also comprises the energy of thermal excitations of the atoms and molecules of the adsorbent?