THERMODYNAMICS OF THE THERMAL-DECOMPOSITION OF CALCIUM-OXALATE MONOHYDRATE EXAMINED THEORETICALLY

Geometries and energies of isolated CaC2O4.H2O, CaC2O4, CaCO3, CaO, H2 O, CO and CO2 were determined at the ah initio level using effective c ore potential valence basis sets of double zeta quality, supplemented with polarization functions. The effects of electron correlation were taken into account at the second order Moller-Plesset level of theory. For CaC2O4.H2O, the correlation for the basis set superposition error was also included. Common routines were employed to evaluate entropie s, heat capacities, as well as enthalpies and free enthalpies of forma tion of all entities. The enthalphies and free enthalpies of consecuti ve dehydration of CaC2O4.H2O, decarbonylation of CaC2O4 and decomposit ion of CaCO3 towards CaO and CO2 were determined on the basis of avail able data from the literature or those predicted theoretically Assumin g that upon all the above mentioned processes the system maintains equ ilibrium, the fractions reacted, enthalpy changes and differential dep endencies of these vs. temperature were derived and compared with expe rimental thermoanalytical data.