In science, Marcellin Berthelot (1827-1907) was a French chemist noted for his 1864 theory, similar Danish chemist Julius Thomsen, that the heat of a reaction was the true measure of affinity and for his 1875 principle of maximum work, both of which were later shown to be incorrect with the development of the science of chemical thermodynamics in the 1880s. [1] Berthelot was a founder of thermochemistry and coined the terms exothermic and endothermic to describe whether heat leaves or is absorbed by a reaction. [4]

The following comment by English chemist Arthur Lamb, translator of the works of German chemist Fritz Haber, on the merit of Haber’s 1907 Thermodynamics of Technical Gas phase Reactions, highlights the view of Berthelot: [2]

“The most important contribution [Haber (1907)] to the subject of predicting the course of a chemical reaction from a few characteristic constants (after the ill-starred attempt of Berthelot).”

In addition to Haber, a number of thermodynamicists, such as Hermann Helmholtz, Walther Nernst, Theophile de Donder, Gilbert Lewis, among others, went to great lengths to disprove Berthelot’s theory, some even wining the Nobel Prize for their efforts.

Maximum work principle

See main: Principle of maximum work

Into the 1870s, the identification of “affinity” or “work” (or maximum work) with the heat alone, according to Berthelot, was to prove erroneous, in that the newly defined quantity entropy (1865) was also a factor. Berthelot's heat theory of affinity was initially criticized by French physicist Pierre Duhem, in a thesis that Berthelot’s colleagues rejected. [3]

Berthelot’s principle of maximum work, however, eventually met its demise with the publication of Helmholtz’ 1882 paper “The Thermodynamics of Chemical Operations”, in which he proved that the affinity is measured not by the heat evolved in a chemical reaction (in a galvanic battery) but by the maximum work produced when the reaction is carried out reversibly. One must distinguish, according to Helmholtz, between that part of energy which appears only as heat and that part which can be freely converted into other kinds of work, i.e. the “free energy” analogous to potential energy in mechanics. Subsequently, the conditions of chemical stability are not determined by heat production but by the production of a decrease in free energy. [3]

See also
● Claude Berthollet (1748-1822) - a French chemist, with a similar last name, who also did work on affinity.

References
1. Thims, Libb. (2007). Human Chemistry (Volume Two) (Marcellin Berthelot, pgs. 434-35, 661, 710, 750) (preview) (Google books). Morrisville, NC: LuLu.
2. Haber, Fritz. (1905). Thermodynamics of Technical Gas Reactions, (Translator’s Preface, 1907, pg. vii). Longmans, Green, and Co.
3. Nye, Mary J. (1993). From Chemical Philosophy to Theoretical Chemistry: Dynamics of Matter and Dynamics of Disciplines: 1800-1950 (section: From Chemical Affinity to Chemical Thermodynamics, pgs. 116-20). University of California Press.
4. Look, Dwight C., Sauer, Harry J., and Alexander, Graham I. (1988). Engineering Thermodynamics (pg. 764). Van Nostrand Reinhold.

External links
● Marcellin Berthelot – Wikipedia.
● Principle of maximum work – Wikipedia.