# Affinity

In chemistry, affinity (TR:512) (LH:7) (TL:519|#58), from Latin affinitas (Latin), from Empedocles philia (φιλία) (445BC), meaning when two of the four elements, symbol "●" (earth, air, water, fire) move towards each other (● → | ← ●), from the Greek letter Phi (Φ) (1100BC), from the Egyptian fire drill and blacksmith god Ptah (2800BC), refers to the "cause of combination" of chemicals (Rodwell, 1873) or the "force with which different chemical substances cling together" (Franklin, 1912).

## Overview

In 445BC, Empedocles introduced the concept of philia (φιλία) (445BC), secret name: "will" (βουλημα) (NE:551), meaning when two of the four elements, symbol "●" (earth, air, water, fire) move towards each other (● → | ← ●), from the Greek letter Phi (Φ) (1100BC), from the Egyptian fire drill and blacksmith god Ptah (2800BC).

In 1250, Albert Magnus, in his Book of Secrets, and other publications, building on Plato's "like attracts to like" principle, originated the concept of "affinitas" (Latin) or affinities, operating as an attractive or reaction principle in chemistry, which he defined in terms of four principles of affinity.

In 1717, Newton, in his "Query 31", introduced a gradient of affinity powers, in respect to reactions between different chemical species, in the sense of the power of the ability of a given species to displace another species from its extant union, by nothing more than proximity.

In 1718, Etienne Geoffroy, expanded the verbal logic of Newton's "Query 31" into the world's first affinity table.

In 1757, William Cullen, in his chemistry lectures, introduced crochets or brackets: " { " to signify a "bond" or attachment uniting two chemical species, and darts: "" or ""to signify the pointing "direction" of the affinity or force guiding a species away from its attached component and to its new preferred bonding direction, i.e. towards a new species, in the course of a chemical reaction.

In 1775, Torbern Bergman, amid the growth of affinity table construction prevalent in the 18th century, built the largest affinity table on record.

In 1809, Goethe, in his Elective Affinities, explained how affinity scales up to and applies to bondings and debondings, and moves towards or away from people, seen in human relationships and in society.

### Transition

In 1790s to 1840s, affinity as a concept in chemistry began to become more complicated. Specifically, with the rise of electrochemistry, the premise of "split affinities" began to appear, in theory. Secondly, with the rise of thermochemistry, the temperature-dependence of reactions became known, meaning that a different affinity table would have to be built for each temperature. Thirdly, the so-called "thermal theory of affinity" arose, which conjectured that the heat released from a chemical reaction was the true "measure" of the affinity.

### Helmholtz

In 1882, Helmholtz, in his "On the Thermodynamics of Chemical Processes", disproved the thermal theory of affinity, replacing it with the new "thermodynamic theory of affinity", wherein the "free energy", not the heat, is the true measure of the affinity.

In 1936, Theophile Donder (CR:76), in his Thermodynamic Theory of Affinity, building on Helmholtz, defined affinity as follows:[1]

${\displaystyle A=-{\frac {\partial G}{\partial \xi }}_{p,T}}$

where A is affinity, ∂ξ is the partial of the Gibbs energy G, ∂ξ is the partial of the reaction extent, p is pressure, and T is temperature, the latter shown in subscript signifying they are being held constant in the differentiation, in respect to the system being an isothermal and isobaric.

In 1940s, affinity began to be defined as follows:

${\displaystyle A=-\Delta G}$

where ΔG is the change, symbol Delta "Δ", in the Gibbs energy G of the system, on going reactants to products, defined as follows:

${\displaystyle \Delta G=G_{F}-G_{I}}$

where GF is the final state Gibbs energy, i.e. the sum of the formation free energies of the products, and GI is the initial state Gibbs energy, i.e. the sum of the formation free energies of the reactants.

## Quotes

The following are related quotes:

Albertus Magnus employs the term affinity (affinitas) to designate the cause of the combination of sulphur with silver and otter metals; in this precise sense, applied to all cases of chemical combination, the term is used in the present day.”
— George Rodwell (1873), “The Birth of Chemistry” (pg. 285)[2]
“If thought is capable of being classified with electricity, or will with chemical affinity, as a mode of motion, it seems necessary to fall at once under the second law of thermodynamics. Of all possible theories, this is likely to prove the most fatal to professors of history.”
Henry Adams (1910), A Letter to American Teachers of History (pg. 101-12)[3]
“Conceptions of chemical affinity date from Albertus Magnus [c.1250], who first suggested the term to denote the force with which different chemical substances cling together. Ideas of affinity have been varied since that time, and have been the subject of much speculation and controversy. In 1718, Geoffroy compiled affinity tables in which he arranged acids and bases in the order of their acidity and basicity, respectively, as compared with some fundamental substance of the opposite kind. In 1772, Beccaria first observed the relation between chemical and electrical action, when he succeeded in obtaining the phenomenon of reduction by the use of the electric spark. Bergman, in 1775, discussed the question of affinity, and stated that certain elementary substances were capable of uniting to form compounds whose chemical stability was a function of only their polar strengths, and while he totally ignored or even discredited the influence of mass, he, nevertheless, appreciably advanced the knowledge of chemical combination.”
— M.W. Franklin (1912), “The Electron Theory” (pg. 27) [4]