|A 2012 short film, entitled “A Strange Thing Called Love”, by Indians Vamshi Regalla and Ravi Vedula, on the thermodynamics of love, from a chemical engineer's point of view, about a guy with 9 girlfriends to choose from to marry, the synopsis of which is: “love is a form of energy that can neither be created nor destroyed”; [first law] “It only gets transferred from one girl to another” [second law].|
The subject of the thermodynamics of love is one of the least studied fields in human thermodynamics, owing to its notorious difficulty. The first to give a pre-thermodynamics dissection of the topic was German polymath Johann Goethe who in 1799 began developing a theory of human chemistry in which human relationships are chemical reactions in which people, as chemical entities, attract and reply, neutralize each other, separate again, and reestablish themselves according to the laws of affinity chemistry or specifically according to the force of chemical affinity, symbol "A". In 1882, German physicist Hermann Helmholtz, in his “On the Thermodynamics of Chemical Processes”, showed that measurement of chemical affinity is the negative of the free energy change; which in modern terminology translated to the fact that for freely going, surface attached, earth-bound reactions, at standard conditions, the following equation is the equation of love:
A = –ΔG
specifically affinity is the negative of the Gibbs free energy change ΔG of of the reaction or process of love, in lay speak.
In 1995, as a chemical engineering thermodynamics student, American engineer Libb Thims began to muse one how one would go about using Gibbs free energy change to predict between the successfulness of two or more potential marriage reactions, between one person and two or more potential mates, similar to how physical chemists use Gibbs free energy measurements to determine the energetic feasibility of all chemical reactions. 
In circa 2000, American physicist Christopher Hirata outlined a similar model to Goethe and Thims, in what he called the “thermochemical approach to relationships”, modelling pairing reactions of college student bodies using an equilibrium constant model. 
|American computational chemist David Hwang's 2001 free energy surface graphs for "favored" and "unfavored" male-female reactions. |
In 2001, American computational chemist David Hwang wrote his article “The Thermodynamics of Love”, for his college magazine, outlining how people combine in pairs according to Gibbs free energy determinants, and was the first to do so graphically, using a reaction coordinate, energy surface diagram, depicting the change in Gibbs free energy of a reacting pair over time. 
In 2009, Indian chemist Surya Pati blogged the article “The Thermodynamics of the Human Bond”, outlining how the attachment of two unattached restless people, defined as “chemical molecules”, will stabilized in a bond owing to a free energy decrease. 
In 2009, science teacher David Ng wrote a song about the thermodynamics of love.
In 2013, Columbian microbiologist and cancer researcher Andres Florez published a blog entitled “Thermodynamics of Love” which attempts a thermodynamics of love conceptualized approach to explain love and relationships via a mixture of John Gottman’s The Mathematics of Love (2005) and protein thermodynamics. 
● Chemistry of love
● Physics of love
1. (a) Thims, Libb. (2007). Human Chemistry (Volume One). Morrisville, NC: LuLu.
(b) Thims, Libb. (2007). Human Chemistry (Volume Two). Morrisville, NC: LuLu.
2. (a) Hirata, Christopher M. (c. 2000). “The Physics of Relationships” (section: Fun), Tapir.Caltech.edu.
(b) Hirata, Christopher M. (2010). "The Physics of Relationships", Journal of Human Thermodynamics, 6(5): 62-76.
3. Hwang, David. (2001). "The Thermodynamics of Love" (PDF), Journal of Hybrid Vigor, Issue 1, Emory University.
4. Pati, Surva P. (2009). “The Thermodynamics of the Human Bond!”, Sep. 09, MentalProjections.Blogspt.com.
5. (a) Florez, Andres. (2013). “Thermodynamics of Love”, Science & Salsa, Blogspot.de, Mar 19.
(b) Florez, Andres. (2014). “Thermodynamics of Love”, Insanitek.net, Feb 3.
(c) Gottman, John M. (2005). The Mathematics of Marriage: Dynamic Nonlinear Models. Bradford Books.