The solid-state coordination reaction of CuCl2. 2H(2)O with 8-hydroxyquinoline (HQ): HQ(s)+CuCl2. 2H(2)O(s)--> Cu(HQ)Cl-2(s)+2H(2)O(l) has been studied by solution calorimetry. The molar dissolution enthalpies of the reactants and the products in 3 mol l(-1) HCl of the solid-solid coordination reaction have been measured using an isoperibol calorimeter. From the results and other auxiliary quantities, the standard molar formation enthalpy of [Cu(HQ)Cl-2,s,298.15 K] at 298.15 K has been derived: Delta(f)H(m)(Theta)(Cu(HQ)Cl-2,s,298.15 K)=-340.12 kJ mol(-1).