The differential heat of gas adsorption on solid surface is often used to determine surface energy heterogeneity. In this paper, the theoretical analysis of irreversible dissociative adsorption on double-site surfaces shows that the change of differential adsorption heat with coverage is strongly dependent on the difference of adsorption activation energies between active sites. Furthermore, it was found that a discontinuous double-site surface can exhibit continuous changes of differential adsorption heat with coverage. This indicates that the distribution functions obtained from the relationship between differential adsorption heat and coverage may provide an incorrect characteristic of surface energetic heterogeneity. (c) 2008 Elsevier B.V. All rights reserved.