In chemistry, thermochemistry is the study and measurements of heat phenomena of chemical reactions and chemical processes. [1]

The work of William Cullen (evaporative refrigeration, 1748), Joseph Black (latent heat, 1761), Richard Kirwan (specific fire, 1777), Joao Magellan (specific heat, 1780), Antoine Lavoisier and Pierre Laplace (reaction calorimetry, 1782), Person (heat capacity, date), Dulong-Petit law (Pierre Dulong and Alexis Petit, 1819), among others, marks the start or at least preliminaries of the subject of thermochemistry.

Science historian Helge Kragh argues that what can be classified as “classical thermochemistry” is was the subject “inextricably bound up with the problem of chemical affinity”, which seems about right, specifically the question of heat (release or absorption) in relation to chemical reaction and the older 18th century theories of chemical affinity, which was said to be the period when Danish chemist Julius Thomsen (1826-1909) began his career. [2]

The hyphenated term “thermo-chemistry” (heat chemistry) was an independent subject in as early as the 1830s and 40s.

The downfall of the heat of reaction theories of Danish chemist Julius Thomsen, i.e. his 1854 "thermal theory of affinity" (Berthelot-Thomsen principle), and French chemist Marcellin Berthelot, i.e. his similar 1864 principle of maximum work, occurred with the publication of German physicist Hermann Helmholtz's 1882 "On the Thermodynamics of Chemical Processes", wherein it was shown that affinity was a function of free energy, and not solely heat.

This years marks the start (or period) of slow integration of thermochemistry into the chemical thermodynamics, an integration that would not be completed until at least the 1920s.

See also
Chemical thermodynamics
● Relationship thermochemistry (Christopher Hirata)

1. (a) Thomsen, Julius. (1905). Thermochemistry. Copenhagen: Publisher.
(b) Thomsen, Julius. (1882). Thermochemische Untersuchungen (Thermochemical Investigations), Volumes 1, 2, 3, 4). Leipzig: Verlag von Johann Ambrosius Barth.
2. Kragh, Helge. (1984). “Julius Thomsen and Classical Thermochemistry” (abs), The British Journal for the History of Science, 17: 255-72.

Further reading
● Horstmann, August. (1899). “Thermochemistry considerations for the Mechanical Theory of Heat”, Lectures.
● Sackur, Otto. (1917). A Textbook of Thermochemistry and Thermodynamics. Publisher.
● Dolby, R.G.A. (1984). “Thermochemistry Versus Thermodynamics: the Nineteenth Century Controversy” (online), History of Science, 22: 375-400.
● Kragh, Helge and Weininger, Stephen J. (1996). “Sooner Silence than Confusion: the tortuous Entropy of Entropy into Chemistry” (abs), Historical Studies in the Physical and Biological Sciences, 27(1): 91-130.

External links
Thermochemistry – Wikipedia.

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