Heat of Formation of Calcium Aluminate Tricarbonate at 25 °C

The heat of formation at 25 °C, $$ = -16,228 kJ/mole, of calcium aluminate tricarbonate, 3CaO·Al₂O₃·3CaCO₃·30H₂O (c), was determined by the heat-of-solution method, with 2N HCl as the solvent, and 3CaO·A1₂O₃· 6H₂O (c) and CaCO₃ (c) as the reactants. The heat of solution in 2N HCl is -501.0 kJ/mole, and the heat of the reaction 3CaO· A1₂O₃. 6H₂O (c) + 3CaCO₃ (c) + 24H₂O (1) →3CaO· A1₂O₃· 3CaCO₃·30H₂O (c) is -186.6 kJ. The rate at which the heat of solution in 2N HCl changes with H₂O content at the 30H₂O level, dv(ΔH)/dn, is + 9.0 kJ/mole per mole H₂O. Heats of solution were determined for samples in the range of 6 to 31H₂O, but decomposition appears to occur on drying to H₂O contents lower than 26H₂O. The heats of stop wise reactions leading to the formation of calcium aluminate mono- and tricarbonate have also been calculated.