In chemistry, the driving force or "force of reaction" is the "chemical affinity" or affinity A of a reaction, which is measured by the decrease in Gibbs free energy on going from the reactants to the products of a chemical reaction (-ΔG). [1] This process, in a colloquial sense, often goes by the shortened term "drive".

History
In affinity chemistry, the elusive quantity 'affinity' (or chemical affinity), a term dating to at least 1150, has long been known as the 'driving force' of chemical reactions and processes. In 1882 and 1884, respectively, German physician and physicist Hermann Helmholtz and Dutch physical chemist Jacobus van’t Hoff, independently, determined that free energy change was the true measure of affinity or the driving force of chemical reactions. [4]

In 1910, American mechanical engineer Joseph Klein, stated that the “change of entropy (ΔS) constitutes the driving motive in all natural events”; and that “it has therefore a reach and universality which even transcends that of the first law or principle of the conservation of energy.” [2]

The origin and logic of the term "driving force", however, stems in large part from the 1923 textbook Thermodynamics and the Free Energy of Chemical Substances, specifically the section "The Driving Force of a Chemical Reaction and a New Test for Equilibrium", by American physical chemists Gilbert Lewis and Merle Randall, which is the most referenced thermodynamics textbook of all-time. [3]

Overview
American physical chemist Ron Salzman explains the concept of 'driving force' by stating that for chemical reactive systems at constant T and p, the Gibbs free energy seeks a minimum; subsequently, one can use ΔG to tell whether or not a reaction will proceed spontaneously as written: [5]

If ΔG > 0 then the reaction will not go as written (the reverse reaction will go)
if ΔG < 0 then the reaction will go as written.

The quantity ΔG, according to Salzman, is a measure of the "driving force" of a chemical reaction; conveying the idea that ΔG tells whether or not a given reaction will really run spontaneously. The two components of the reaction "driving force", according to Salzman, are:

ΔH is the drive toward stability. When ΔH < 0 the products are more stable than the reactants (and vice versa).
ΔS is the drive toward disorder. When ΔS > 0 the products are more disordered than the reactants.

In the expression for Gibbs free energy change:

ΔG = ΔH – TΔS

the negative sign in front of the ‘TΔS’ product shows that a positive ΔS makes a negative contribution to ΔG which tends to drive the reaction in the forward direction. One should note, according to Salzman, that increasing T increases the influence of ΔS on the reaction "driving force"; also, that for a chemical reaction, ΔH and ΔS are independent of each other; that is, one cannot be calculated from the other. Reactions can also have situations where both are positive, both are negative, or one is positive and the other negative. It should be noticed, according to Salzman, that if ΔH and ΔS have the same sign, it means crudely that they are energetically working against each other. A good rule, according to Salzman, is that one can make the entropy win by increasing the temperature or you can make the enthalpy win by decreasing the temperature.

See also
● Affinity of reaction

References
1. (a) Keii, Tominaga. (2004). Heterogeneous Kinetics: Theory of Ziegler-Natta-Kaminsky (Volume 77 of Springer series in Chemical Physics) (2.3: Chemical Affinity: Thermodynamic Force of Reaction, pgs. 12-15). Springer.
(b) Driving force (affinity) of a reaction – IUPAC Gold Book.
2. Klein, Joseph Frederic. (1910). “Physical Significance of Entropy or of the Second Law”, (pg. 2). New York: D. Van Nostrand Co.
3. Lewis, Gilbert N. and Randall, Merle. (1923). Thermodynamics and the Free Energy of Chemical Substances, (pg. 159-61). New York: McGraw-Hill Book Co., Inc.
4. (a) van’t Hoff, Jacobus H. (1884). Études de Dynamique chimique ("Studies in Chemical Dynamics"), Amsterdam: F. Muller & Co.
(b) Helmholtz, H. v. "Die Thermodynamic Chemischer Vorgange," (The Thermodynamics of Chemical Operations) SB, pg. 23, pg. 22-29, in Wissenschaftlich Abhandlundgen von Hermann von Helmholtz. 3 vols. Leipzig: J.A. Barth, 1882-95.
5. Salzman, W. Ron. (2004). “Gibbs free energy and Reactions”, Physical Chemistry, University of Arizona.