The kinetics and thermodynamics of dehydration and intermolecular polycondensation reactions of Mn1/2Fe1/2(H2PO4)(2)center dot H2O and Mn1/2Fe1/2(H2PO4)(2) were studied under nonisothermal heating by thermogravimetry (TG). On the basis of three calculation procedures and 24 kinetic mechanism functions, kinetic triplets (E, A, kinetic model) using the Arrhenius equation were calculated for both processes. The comparison of the results obtained with these calculation procedures show a strong dependence oil the selection of the mechanism function for the process. The thermodynamic functions (Delta H*, C-p, Delta G*, and Delta S*) of both reactions are calculated from differential scanning calorimetry (DSC) experiments. Kinetic and thermodynamic results indicate that the polycondensation step has a lower rate and is I stronger reaction than the dehydration step and corresponds to the breaking of the strong hydrogenbonded P-OH group, in Connection With the polycondensation reaction, which confirms that the decomposition product (manganese iron cyclotetraphosphate, MnFeP4O12) was obtained.