ZnO nanoweeds were prepared by a simple microemulsion-mediated hydrothermal route. SEM observation revealed that each weed consisted of several nanowires which were about 1 mu m in length and 40 nm in diameter. In order to associate thermodynamic functions of nano ZnO with bulk ZnO, a novel thermochemical cycle was designed. Combined with in situ microcalorimetry, the standard molar enthalpy of formation, standard molar Gibbs free energy of formation and standard molar entropy of the obtained products at 298.15K were successfully acquired as (-319.10 +/- 0.42) kJ mol(-1), (-318.53 +/- 0.03) kJ mol(-1) and (54.85 +/- 1.02) J mol(-1) K(-1), respectively. It can be concluded that the striking differences between thermodynamic functions of nano ZnO and bulk ZnO can be rooted to surface effect of nano material. (C) 2011 Elsevier B.V. All rights reserved.