Thermochemistry of teepleite

The enthalpy of solution of teepleite, Na2B(OH)4Cl, in approximately 1 mol dm−3 aqueous hydrochloric acid was determined. Together with the previously determined enthalpies of solution of H3BO3 in approximately 1 mol dm−3 HCl(aq), and of NaCl in aqueous (hydrochloric acid+boric acid), the standard molar enthalpy of formation of −2007.98±0.84 J K−1 mol−1 for Na2B(OH)4Cl was obtained from the standard molar enthalpies of formation NaCl(s), H3BO3(s), and H2O(l). The standard molar entropy of formation of −700.59 J K−1 mol−1 and standard molar entropy of 190.62 J K−1 mol−1 for Na2B(OH)4Cl were calculated from the thermodynamic relations. The group contribution method by Li is applicable to teepleite.