|A depiction of the "free energy" component of the equation for the Helmholtz free energy.|
In 1942, American physical chemist Hugh Taylor stated the following about free energy: 
In isothermal-isobaric systems, free energy is called "Gibbs free energy". In isothermal-isochoric systems, free energy is called "Helmholtz free energy".
The term free energy, or freie energie in the original German, was introduced in German physicist Hermann Helmholtz' 1882 article "The Thermodynamics of Chemical Processes", a term he modeled or stylized on the earlier term "available energy" used in 1876 by American engineer Willard Gibbs.  Helmholtz conceived of "bound energy" (gebundene energie) and "free energy" in thermodynamic systems, and showed that the quantitative value of free energy in a reactive chemical system was a measure of the chemical "affinity" between the reactants. 
Helmholtz's 1882 was spurred into publication out of the growing incorrectness being pushed forward that the release of heat acts as the true driving force of a chemical reaction, i.e. the so-called Berthelot-Thomsen principle (1854-64). Helmholtz proved that, owing to the aspects of entropy, it is the free energy, not heat that is the measure affinities. This is the same article in which the term free energy was coined. The Berthelot-Thomsen principle, to note, still held sway in the minds of many, such as James Johnstone (1921), into the early 20th century. 
In human chemical reactions, which are constant temperature (isothermal), constant pressure (isobaric), surface chemistry reactions, it is the the Gibbs free energy is the quantity of importance.  Changes in the value of free energy can be used to determine if a reaction is thermodynamically favorable. 
The first systematic study of all the thermodynamic date necessary for the calculation of the free energy changes in a group of important reactions was published in Germany by Fritz Haber in his 1905 Thermodynamics of Technical Gas Phase Reactions. 
Others following Haber include: German physical chemist Walther Nernst, Danish physical chemist Johannes Bronsted, and Americans Arthur Noyes, Merle Randall and Gilbert Lewis. 
Some argue that American physicist John Kirkwood, a protégé of Noyes, laid the foundations for the standard method for estimating free energy differences, namely perturbation theory and thermodynamic integration, by building on the chemical affinity and extent of reaction work of Theophile De Donder. Others to have furthered this approach include: Robert Zwanzig, Lev Landau, and Benjamin Widom. 
Perutz | Schrodinger
In 1987 commentary on Erwin Schrödinger’s 1944 book What is Life? (see: Note to Chapter 6) and his ideas on life and "negative entropy", Austrian-born English molecular biologist Max Perutz argued that we live on free energy and that there is no need to postulate the conception of negative entropy. 
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11. Johnstone, James. (1921). The Mechanism of Life in Relation to Modern Physical Theory (pg. ix). Longmans, Green & Co.
● ChemGuy. (2008). “Free Energy” (Ѻ), ChemGuy.com, Jan 4.
● Free energy – Wikipedia.