Thermochemistry of 2MgSO4·MgO·3H2O

The enthalpy of dissolution of magnesium oxysulfate compound 2MgSO4·MgO·3H2O in approximately 1 mol dm−3 aqueous hydrochloric acid was determined. From this result and the enthalpies of dissolution of MgSO4·7H2O and MgO in the same solvent and the standard molar enthalpies of formation of MgO(s), MgSO4·7H2O(s) and H2O(l), the standard molar enthalpy of formation of 2MgSO4·MgO·3H2O (−4132.07 ± 0.57 kJ mol−1) was calculated. The standard molar entropy of formation of 2MgSO4·MgO·3H2O was calculated from the thermodynamic relation with the standard molar Gibbs free energy of formation of 2MgSO4·MgO·3H2O that was computed from a group contribution methods.