Thermochemistry of dipotassium calcium octaborate dodecahydrate

The enthalpies of solution of K2O . CaO . 4B(2)O(3). 12H(2)O in approximate ly 1 mol dm(-3) aqueous hydrochloric acid, and of KCl in aqueous (hydrochlo ric acid+boric acid+calcium oxide) were determined. Together with the previ ously determined enthalpies of solution of H3BO3 in approximately 1 mol dm( -3) HCl(aq), and of CaO in aqueous (hydrochloric acid+boric acid), the stan dard molar enthalpy of formation of -(10308.00+/-6.56) kJ mol(-1) for K2O . CaO . 4B(2)O(3). 12H(2)O was obtained from the standard molar enthalpies o f formation of CaO(s), H3BO3(s), KCl(s), and H2O(l). The standard molar ent ropy of formation of K2O . CaO . 4B(2)O(3). 12H(2)O was calculated from the thermodynamic relation with the standard molar Gibbs free energy of format ion of K2O . CaO . 4B(2)O(3). 12H(2)O computed from the group contribution method. (C) 1999 Elsevier Science B.V. All rights reserved.