In science, exothermic, from the Greek –exo “outside” + -therme heat, warm”, as compared to endothermic, refers to a transformation, i.e. process, reaction, or change of state, wherein heat is released out of the system into the surroundings; formulaically:


If the reaction occurs at constant pressure (isobaric), then ΔH < 0; if the reaction occurs at constant volume (isochoric), then: ΔU < 0. If the system undergoes a transformation which is both exothermic and adiabatic, then its temperature increases.

The term “exothermic”, in French as exothermique, was in use as early as 1851 (Ѻ); it is oft-cited that Marcellin Berthelot coined both “exothermic” and “endothermic”. [2]

The following are related quotes:

“Is hell exothermic or endothermic?”
— Anon (c.1990), said to have been asked on a chemistry mid-term exam; related to Paul Foote’s circa 1920 article “The Temperature of Heaven and Hell” (see: thermodynamics of hell)

1. Perrot, Pierre. (1998). A to Z of Thermodynamics (pg. 108). Oxford University Press.
2. (a) Anon. (1985). Academic American Encyclopedia, Volume 4 (pg. 327). Grolier.
(b) Luck, Steve. (1998). The American Desk Encyclopedia (pg. 96). Oxford University Press.

External links
Exothermic – TheFreeDictionary.com.

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