Heat of Formation of Calcium Aluminate Monocarbonate at 25 °C

The heat of formation of 3CaO·Al₂O₃·CaCO₃·10.68H₂O at 25 °C was determined by the heat-of-solution method, with 2N HCl as the solvent and 3CaO·Al₂O₃·6H₂O and CaCO₃ as the reactants. The heat of solution of CaCO₃, to form dissolved CO₂, was obtained by a new technique and a modified calculation which served to include the heat of vaporization of the gas escaping in the reaction and resulted in a higher value than those obtained by Wells and Tayıor and by Bäckström in determinations representing only partial solution of CO₂. The results obtained were: kj/mole kcal/mole3CaO·Al₂O₃·CaCO₃·10.68H₂O Heat of formation  from elements, $$ -1956     from reactants and H₂O-18.9 Heat of solution in 2N HCl-532.9-127.43CaO·Al₂O₃·6H₂O Heat of solution in 2N HCl-576.6-137.8CaCO₃ Heat of solution in 2N HCl-35.0-8.4.