The role of calorimetry in adsorption is shortly reviewed. The differences between calorimetric adsorption heats and those calculated from Clausius-Clapeyron equation for the systems ethanol-activated carbons are presented. Obtained results, together with the results presented previously for other adsorbates, confirm that calorimetry is indispensable for a real thermodynamical description of the adsorption process in this type of system.