Kirchhoff's Law
The relation describing how the enthalpy change of a reaction varies with temperature.
Formula / equation
ΔH(T₂) = ΔH(T₁) + ΔC_p(T₂ − T₁)
Unit
kJ/mol
In depth
Because products and reactants have different heat capacities, warming both sides changes their enthalpies by different amounts and so shifts ΔH. The correction matters whenever tabulated 298 K data must be applied to an industrial process running hundreds of degrees hotter.
Examples in the real world
Adjusting the ammonia synthesis enthalpy from 298 K to the 700 K of a real Haber reactor.