Activation energies of thermal decomposition processes of MgBr₂.6H₂O

The activation energies of thermal decomposition processes of MgBr₂.6H₂O were studied by applying Kissinger's method to DTA and DTG curves. The activation energy of dehydration appeared to be higher for the hexahydrate (43 kcal.mole^-1, or 180 kJ.mole^-1) than for the dihydrate (31.5 kcal.mole^-1, or 132 kJ.mole^-1). This may be attributed to the fact that the large [Mg(H₂O)₆]²⁺ cation is more stable in the Br^- sub-lattice than the relatively small [Mg(H₂O)₂]²⁺ cation.