In famous publications, "The Thermodynamics of Love" is a 2001 article, published in the Journal of Hybrid Vigor, by American computational chemist David Hwang, in which a Gibb free energy theory of mate selection is outline, albiet in humorous form. [1] In short, in chemistry, reaction feasibility is determined by "thermodynamics", particularly chemical thermodynamics. Subsequently, the feasibilities of the various potential processes of human mating or "love the chemical reaction" would also be determined by thermodynamics. A popular 2003 internet quote that elaborates on this premise comes from internet writer Wild Bob in his short article “Thermodynamics of Love”. He reasons, “people often can be heard talking about the 'chemistry' in a relationship. Chemistry may be involved in the initial attraction, but it is thermodynamics that determines if the relationship will last.” Without going into too much detail on this postulate, he concludes: [2]


Hwang's human thermodynamics
Hwang, however, did more than verbially justify his thermodynamics of love theory, he described it, in rather descent form, from a chemical thermodynamic point of view. [3] In particular, thermodynamics, according to Hwang, "not only explains the spontaneity of chemical reactions", but "also applies directly to various factors determining the success of human relationships". To begin with, Hwang defines the couple forming reaction as such: a theoretical chemical reaction where two elements, "male" (M) and "female" (F), combine to form a new compound called "couple" (M-F):

M + F → M-F

To visually illustrate this, Hwang used free energy vs. reaction extent plots (shown adjacent). Firstly, in regards to the plots, he states that the y-axis measures Gibbs free energy and that the x-axis measures the time progression of the reaction, Hwang defines individual elements (presumably either single unattached people or bonded couples) with a collective high free energy (G) value are relatively reactive, while a compound with a low G value is likely to be stable.

Thus, according to Hwang, a reaction in which G decreases (-sG) favors formation of product because the products have less free energy than the starting compounds and are more stable. In a reaction in which G increases (+sG), in Hwang’s view, reactants are not likely to make much chemical progress. Subsequently, according to Hwang, we can apply these concepts to our theoretical male-female reaction and thus use chemical thermodynamics to answer questions such as “are two people completely natural as a pair, or are they better off apart?”

Difficulties on theory
All-in-all, aside from a few points of argument, Hwang's take on the situation is fairly accurate. One area of difficulty in Hwang's theory is the small particle count aspect involved in the thermodynamic computations of interactions between people with systems consisting of a few humans (e.g. ten human molecules in a system). Specifically, how do the laws of thermodynamics apply to the analysis of, for instance, two particle systems, such as two people in a regioned system? General thermodynamic analysis, e.g. gas phase systems, for instance, studies "working bodies" consisting of Avogadro's number of particles, namely 10E23 particles, i.e. atoms or molecules. There have, however, been thermodynamic studies on one-particle systems. This is an advanced topic.

References
1. Hwang, David. (2001). "The Thermodynamics of Love", Journal of Hybrid Vigor, Issue 1, Emory University.
2. (a) What is Love (top 150 definitions) – Institute of Human Thermodynamics. (b) Wild Bob. (2003). “Thermodynamics of Love”, UnsolvedMysteries.com
3. (a) Thims, Libb. (2007). Human Chemistry (Volume One), (ch. 4: section: "Love and the Combined law of Thermodynamics", pgs. 116-19), (preview), (Google books). Morrisville, NC: LuLu.
(b) Thims, Libb. (2007). Human Chemistry (Volume Two), (pgs. 673-74). (preview), (Google books). Morrisville, NC: LuLu.
(c) Thims, Libb. (2008). The Human Molecule, (pg. 62), (preview). Morrisville, NC: LuLu.