Coupled reactions

Coupled reactions (Caddyshack diagram)
The Caddyshack social coupling diagram, lecture part 12 (ΡΊ), from Libb Thims' 2015 "Zerotheism for Kids" lecture, illustrating coupled reactions in social terms, via the example of nepotism, from the 1980 film Caddyshack.
In science, coupled reactions are two or more reactions, at least on being endergonic (energy requiring), one or more of the others being exergonic (energy yielding), which are "coupled" thermodynamically such that the exergonic reactions drive or power the endergonic reactions, such that the system of reactions or processes as a whole "goes", i.e. occurs naturally.

Overview
In circa 1890s, German physical chemist Wilhelm Ostwald, according to energetics historian John Edsall (1974), was the first, apparently, to discuss coupled reactions, whereby, to use modern terminology (Ostwald used some type of general “energetics” conceptual terminology), the free energy released by an exergonic process can be used to drive an endergonic process that would not go by itself. [1]

In 1920 to 1936, Belgian physical chemist Theophile de Donder was discussing coupled reactions, thermodynamically, in terms of affinity theory. [2]

Quotes
The following are related quotes:

“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.”
John Edsall (1958), Biophysical Chemistry [3]

References
1. Edsall, John T. (1974). “Some Notes and Queries on the Development of Bioenergetics. Notes on some ‘Founding Fathers’ of Physical Chemistry: J. Willard Gibbs, Wilhelm Ostwald, Walther Nernst, Gilbert Newton Lewis” (abs), Molecular and Cellular Biochemistry, 5(1-2): 103–12, Nov 15.
2. De Donder, Theophile and Van Rysselberghe Pierre. (1936). Thermodynamic Theory of Affinity: A Book of Principles (pg. 2; affinity coupling, pg. 113). Oxford University Press.
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.

Further reading
● Crofts, Antony. (2009). “Coupled reactions” (lecture 5), Biophysics 354. Illinois.edu.

External links
● Coupled reactions – Wiley.com.
● What is a coupled reaction? (2012) – StackExchange.com.

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