# Kirchhoff's Equation

## Kirchhoff’s Equation

an equality expressing the temperature dependence of the thermal quantities associated with a chemical reaction through the difference in heat capacities between the products and reactants. Specifically, for reactions occurring at constant volume, Kirchhoff’s equation relates the temperature dependence of the change in internal energy *ΔU* of a reaction to the difference in isochoric heat capabilities *C _{ν}* in the following form:

where *C _{v,1}* and

*C*are the sums of heat capacities of the reactants and products taking into account their stochiometric coefficients in the reaction equation. By integrating this equation, it is possible to determine the change in internal energy

_{v,2}*ΔU*at the temperature of interest

_{T}*T*if the following are known:

*ΔU*at some other temperature

_{T1}*T*and the heat capacities of the reactants and products for the temperature range in question. Kirchhoff’s equation was deduced by G. R. Kirchhoff in 1858.

_{1}V. A. KIREEV