The decomposition kinetics of solids, part 2: Thermodynamic evidence for the enthalpy driven cooling of reaction environment

The analysis of non-isothermal kinetic data for the decomposition of calcium carbonate, CaC03 (s) -> CaO (s) + CO2 (g) in flowing nitrogen, shows that the decomposition of solids is accompanied by self-cooling/heating of the reaction environment depending on the sample mass and heating rate. The correctness of the kinetic model is established by the calculation of the enthalpy change of the reaction. This is the thermodynamic evidence of endothermic enthalpy driven cooling of the reaction environment. The enthalpy change ?H = 179.33 kJmol-1 estimated from this work for the dissociation of CaCO3 is in agreement with ?H = 179.17 kJmol-1 derived from the enthalpies of formation of the reaction components. The results support the mechanism suggesting heat transport to be the rate-limiting step.