In colloquial sense, love is a word that describes various states of positive emotional experiences, that encompass a number of facets of human activity, particularly the desire to give one's life to another person, as well as the combined acts of caring, friendship, family, and intimate union. [1]

Human chemistry
In human chemistry, love is an umbrella term that encompasses the overall emotional and energetic evolution state of the process of a spontaneous combination reaction between two human molecules, in which commonly two previously unattached people, A and B, collided in life to unite in the form of a dynamic AB couple: [2]

A + B → AB

The word "love", however, is intimately linked to the word "hate", particularly in reference to chemical bonding dynamics. Namely, when the term love is used to signify a certain level of attraction to a quality of a person, object, or objective, and conversely when the word hate is used to signify a certain level of repulsion to the same person, object, or objective, then the two labels function as balancing stabilizers in the bond, as found, for instance, in a 5-to-1 ratio in long term marriage bonds. [3]

Human Thermodynamics
In human thermodynamics, love is a term that is quantified by the release of functional or usable work energy, particularly Gibbs free energy, out of a thermodynamic system during an evolution cycle. One of the first to write semi-correctly about the thermodynamics of love was American computational chemist David Hwang in his 2001 article "The Thermodynamics of love". [4]

Entropy
Some have postulated a relationship between love and entropy. According to American economist Jeremy Rifkin, for instance, “Love is not antientropic, as some would like to believe. If love were antientropic, it would be a force in opposition to becoming, for the entropic flow and becoming go hand in hand. Rather, love is an act of supreme commitment to the unfolding process. That is why the highest form of love is self-sacrifice—the willingness to go without, even to give one’s own life, if necessary, to foster life itself.” [5]

References:
1. Top 150 Definitions of Love - Institute of Human Thermodynamics
2. Thims, Libb. (2007). Human Chemistry (Volume One), (preview). Morrisville, NC: LuLu.
3. Gottman, John. (1994) Why Marriages Succeed or Fail. New York: Fireside.
4. Hwang, David. (2001). "The Thermodynamics of Love", Journal of Hybrid Vigor, Issue 1, Emory University.
5. Rifkin, Jeremy. (1989). Entropy - Into the Greenhouse World (formerly published as Entropy: a New World View, 1981), (pg. 291). New York: Bantam Books.