Abstract: The enthalpy changes on mixing and reaction between synthetical MgO-27.56%MgCl₂-H₂O solution and azeotropic hydrochloric acid have been studied with a precisecalorimeter. It is shown that the active magnesium oxide has different thermochemical be-havior in 27. 56%MsCl₂-H₂O solution. When the concentration of MgO is≤0.8914mmol(50mL solution)the molar enthalpy of MgO is almost identical small than when the concen-tration is higher. A mechanism for the reaction has been proposed in combination the resultswith that obtained in azeotropic hydrochloric acid-pH titration.

Key words: MgO, aqueous magnesium chloride solution, azeotropic hydrochloric acid reac-tion.reaction mechanism.calorimetric titration