Abstract

Enthalpies of formation, Delta H, of the double carbonates K 2 Ca(CO 3 ) 2 (with two polymorphs, butschliite and fairchildite) and K 2 Ca 2 (CO 3 ) 3 from the components K 2 CO 3 and CaCO 3 were determined at 298 K by drop solution calorimetry in molten 2PbO.B 2 O 3 at 974 K. The enthalpies of formation were -38.7+ or -3.2 kJ/mol for butschliite. -5.1+ or -3.3 kJ/mol for fairchildite and -7.2+ or -5.8 kJ/mol for K 2 Ca 2 (CO 3 ) 3 . The entropy changes for the formation. Delta S f , were also evaluated for the double carbonates. Assuming Delta S f (butschliite) = 0, because of its ordered structure, the entropy of formation of fairchildite is 40.9+ or -5.1 J/mol.K and of K 2 Ca 2 (CO 3 ) 3 is 39.4+ or -7.3 J/mol.K.

You do not currently have access to this article.