
A circa 1940 article (Ѻ) using "exergonic" per so-called "Coryell terminology", i.e. that of American chemist Charles Coryell, as reactions that yield energy that can be used to do work, e.g. muscular work, i.e. the shortening of the myosin fiber.

A circa 1940 article (Ѻ) using "exergonic" per so-called "Coryell terminology", i.e. that of American chemist Charles Coryell, as reactions that yield energy that can be used to do work, e.g. muscular work, i.e. the shortening of the myosin fiber.

In thermodynamics, exergonic, from the Greek exo- “turning out” + -ergon “work”, as contrasted with endergonic, refers to a free energy or available energy releasing process or reaction, one in which work energy is produced, so to speak, defined by the criterion: ΔG < 0 (isothermal, isobaric process) or ΔF < 0 (isothermal, isochoric process). In short, an exergonic reaction (or process) requires no energy to proceed. [1]

Etymology
In 1940, American chemist Charles Coryell, in his Science letter “The Proposed Terms ‘Exergonic’ and Endergonic’ for Thermodynamics”, introduced the terms ‘exergonic’ (energy-yielding) and ‘endergonic’ (energy-requiring), as definitive of reactions that provide free energy, and so can produce work, as opposed to reactions which work must be expended to cause the reactions to go. [1]

Coryell, in short, proposed (Ѻ) the terms “exergonic”, for spontaneous (ΔG negative) processes or reactions, i.e. those which can produce work (Ѻ), and “endergonic”, for non-spontaneous (ΔG positive) processes or reactions, i.e. those which cannot produce work, on “analogy”, according to John Edsall and Jeffries Wyman (1958), with “exothermic” and “endothermic”, introduced in the 19th century by Marcellin Berthelot. Edsall and Wyman summarize this logic as follows: [3]

“For a total process it is impossible to escape the rigorous requirement that the total free energy change, at constant pressure and temperature, must be negative if the process is to go. Such spontaneous processes (ΔG negative) have been termed ‘exergonic’ by Charles Coryell, in analogy to the term exothermic for processes in which ΔH is negative. A process which taken alone would be endergonic (ΔG positive), and therefore thermodynamically forbidden, may nevertheless proceed if it is coupled with another process which is so highly exergonic that the total value of ΔG for the combined reaction is negative. Such coupled reactions are of profound importance in biochemistry. The supply of free energy in many coupled biochemical reactions is provided by the hydrolysis of adenosine triphosphate (ATP to adenosine diphosphate (ADP) and inorganic phosphate.”

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Quotes
The following are related quotes:

“Other [non-photosynthesizing] living forms must obtain energy from living forms must obtain energy from exergonic chemical reactions.”
— Author (1950), “Article” (Ѻ)

References
1. Purves, William K, Sadava, David, and Orians, Gordon H. (2004). Life: the Science of Biology (section: ATP couples exergonic and endergonic reactions, pgs. 112-13). MacMillian.
2. Coryell, Charles D. (1940). “The Proposed Terms ‘Exergonic’ and Endergonic’ for Thermodynamics” (Ѻ), Science, 92:380, Oct.
3. Edsall, John T. and Wyman, Jeffries. (1958). Biophysical Chemistry: Thermodynamics, Electrostatics, and the Biological Significance of the Properties of Matter (pg. 210). Academic Press.

External links
● Exergonic – Wikipedia.