In thermodynamics and physical chemistry, thermochemistry is the study of the heat evolved or absorbed in chemical reactions. Thermochemistry, generally, is concerned with the heat exchange accompanying transformations, such as mixing, phase transitions, chemical reactions, etc., which includes calculations of such quantities as the heat capacity, heat of combustion, heat of formation, etc. The laws of thermochemistry rest on two statements:[1]
Both laws preceded the first law of thermodynamics (1850); it can be shown, however, that they are a direct consequence of it.
They also investigated specific heat and latent heat.