We established, for the first time, the increase of oxidation enthalpies of carbon particles with decreasing grain sizes, i.e. the depression of cohesive energy of nanoparticles due to dangling chemical bonds on the surface. This effect enhances chemical reactivity of nanophases. Thus, the Cu, C, Si, Ge and Pt nanoparticles interact with water at room temperature, replacing hydrogen. (C) 2017 Elsevier B.V. All rights reserved.