LawKirchhoff's Law of ThermochemistryThe variation of the heat of reaction with temperature is given by the difference in heat capacities of products and reactants: ΔHT2=ΔHT1+∫T1T2ΔCpdT\Delta H_{T_2} = \Delta H_{T_1} + \int_{T_1}^{T_2} \Delta C_p dTΔHT2=ΔHT1+∫T1T2ΔCpdT.