Four tensimetric methods were used to measure the equilibrium water vapour pressure for the reaction 1/2CuCl(2)center dot 2H(2)O(s) = 1/2CuCl(2)(s) + H2O(g) in the temperature range (301.40 to 404.65) K. Formation of the metastable hydrate super disperse phase [O.G. Polyachenok, E.N. Dudkina, N.V. Branovitskaya, L.D. Polyachenok, Thermochim. Acta 467 (2008) 44-53] was taken into account at studying this process. A linear equation was derived for the temperature dependence of the water vapour pressure: In(p/ p(o)) = 17.237 - 6980.4 . (K/T). Standard enthalpy and entropy of this process were calculated at the mean temperature 358 K: Delta H-r(o)(358) = 58038 +/- 73 J, Delta S-r(o)(358) = 143.32 +/- 0.21 J . K-1. These data being processed together with the results of [R.Perret, Bull. Soc. Chim. France 2 (1966) 755-758] enabled to obtain the change of heat capacity Delta C-r(p)o = -10 +/- 2J . K-1 . mol(-1), and hence a more precise trinomial equation was deduced: In(p/p(o)) = 25.515 - 7409.4 . (K/T) -1.203 - In(T/K). Standard thermodynamic characteristics of copper(II) chloride and its dihydrate were obtained: Delta H-r(m)o (298)CuCl2(s) = -219.1 +/- 1.8 kJ . mol(-1): S-m(o)(298)CuCl2 . 2H(2)O(S) = 195.3 +/-1.4 J . K-1 . mol(-1); C-p,m(o)(298)CuCl2 . 2H(2)O(s) = 159 +/- 4 J . K-1 mol(-1). (C) 2008 Elsevier Ltd. All rights reserved.