Thermochemistry of dicesium calcium tetraborate octahydrate

Abstract The enthalpies of solution of Cs 2 Ca[B 4 O 5 (OH) 4 ] 2 ·8H 2 O(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 H 3 BO 3 (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 Cs 2 Ca[B 4 O 5 (OH) 4 ] 2 ·8H 2 O(s) was obtained from the standard molar enthalpy of formation of CaO(s), CsCl(s), H 3 BO 3 (s) and H 2 O(l). The standard molar entropy of formation of Cs 2 Ca[B 4 O 5 (OH) 4 ] 2 ·8H 2 O(s) was calculated from the thermodynamic relation with the standard molar Gibbs free energy of formation of Cs 2 Ca[B 4 O 5 (OH) 4 ] 2 ·8H 2 O(s) computed from a group contribution method.