Editing Gustav Kirchhoff (section)

=== Kirchhoff's law of thermochemistry ===
{{see also|Standard enthalpy of reaction#Variation with temperature or pressure}}
Kirchhoff showed in 1858 that, in [[thermochemistry]], the variation of the [[Standard enthalpy of reaction|heat of a chemical reaction]] is given by the difference in [[heat capacity]] between products and reactants:

:<math>\left(\frac{\partial \Delta H}{\partial T}\right)_p = \Delta C_p</math>.

Integration of this equation permits the evaluation of the heat of reaction at one temperature from measurements at another temperature.<ref>[[Keith J. Laidler|Laidler, Keith J.]]; and Meiser, J. H.; "Physical Chemistry", Benjamin/Cummings 1982, p. 62</ref><ref>[[Peter Atkins|Atkins, Peter]]; and de Paula, J.; "Atkins' Physical Chemistry", W. H. Freeman, 2006 (8th edition), p. 56</ref>