Thermochemistry of dicesium calcium tetraborate octahydrate

The enthalpies of solution of Cs2Ca[B4O5(OH)4]2·8H2O(s) in approximately 1 mol dm−3 aqueous hydrochloric acid and of CsCl(s) in aqueous (hydrochloric acid + boric acid + calcium oxide) were determined. From these results and the enthalpies of solution of H3BO3(s) in approximately 1 mol dm−3 HCl(aq) and of CaO(s) in aqueous (hydrochloric acid + boric acid), the standard molar enthalpy of formation of −(10328 ± 6) kJ mol−1 for Cs2Ca[B4O5(OH)4]2·8H2O(s) was obtained from the standard molar enthalpy of formation of CaO(s), CsCl(s), H3BO3(s) and H2O(l). The standard molar entropy of formation of Cs2Ca[B4O5(OH)4]2·8H2O(s) was calculated from the thermodynamic relation with the standard molar Gibbs free energy of formation of Cs2Ca[B4O5(OH)4]2·8H2O(s) computed from a group contribution method.