‎"KIRCHHOFF, G. (GUSTAV ROBERT). - KIRCHHOFF'S LAW OF THERMOCHEMISTRY ANNOUNCED.‎
‎Ueber einen Satz der mechanischen Wärmetheorie, und einige Anwendungen desselben. (+) Bemerkung über die Spannung des Wasserdampfes bei Temperaturen, die dem Eispunkte nahe sind.‎

‎(Leipzig, Johann Ambrosius Barth, 1858). Without wrappers. In ""Annalen der Physik und Chemie. Hrsg. von J.C. Poggendorff"", Bd. 103, No 2. Pp. 177-352 a. 1 folded engraved plate. (Entire issue offered). Kirchhoff's papers: pp. 177-206 a. pp. 206-209.‎

Reference : 45717

‎First appearance of this importent paper on the mechanical equivalent of heat in which Kirchhoff showed that the variation of the heat of a chemical reaction is given by the difference in heat capacity between products and reactants in an equation. Integration of his equation permits the evaluation of the heat of reaction at one temperature from measurements at another temperature.Kirchhoff's Law describes the enthalpy of a reaction's variation with temperature changes. In general, enthalpy of any substance increases with temperature, which means both the products and the reactants' enthalpies increase. The overall enthalpy of the reaction will change if the increase in the enthalpy of products and reactants is different. ‎