STANDARD ENTHALPIES OF FORMATION OF ANHYDROUS AND AQUEOUS MAGNESIUM-CHLORIDE AT 298.15-K

Enthalpies of solution of MgCl2(c) in hydrochloric acid solution of composition, 77.2HCl + 4190H2O, and in pure water have been measured. The measurements for acid solution have been combined with additional data from the literature to establish a new value for the enthalpy of formation of the crystal: ΔHfo(MgCl2, c, 298.15 K) = -(644.28 ± 0.69) kJ mol-1. From the measurements in pure water, the standard enthalpy of solution was evaluated, and this value was used with the new enthalpy of formation for MgCl2(c) to obtain ΔHfo(MgCl2, aq, 298.15 K) = -(800.12 ± 0.89) kJ mol-1. Combination of this with ΔHfo(Cl-, aq, 298.15 K) leads to ΔHfo(Mg2+, aq, 298.15 K) = -(465.96 ± 1.07) kJ mol-1. © 1979.