Chemical affinity
In physical chemistry, chemical affinity, historically, refers to the "force" that causes
chemical reactions. In current use, it can be defined as electronic properties by which dissimilar chemical species are capable of forming chemical compounds. Chemical affinity can also refer to the tendency of an
atom or compound to combine by
chemical reaction with atoms or compounds of unlike composition. The following statement, made by Ilya Prigogine, summarizes the concept of affinity:
The term
affinity has been used figuratively since c.1600 in discussions of structural relationships in chemistry, philology, etc., and reference to "natural attraction" is from 1616.
Encyclopedia
In physical chemistry,
chemical affinity, historically, refers to the "force" that causes
chemical reactions. In current use, it can be defined as electronic properties by which dissimilar chemical species are capable of forming chemical compounds. Chemical affinity can also refer to the tendency of an
atom or compound to combine by
chemical reaction with atoms or compounds of unlike composition. The following statement, made by Ilya Prigogine, summarizes the concept of affinity:
The term
affinity has been used figuratively since c.1600 in discussions of structural relationships in chemistry, philology, etc., and reference to "natural attraction" is from 1616. According to chemistry historian Henry Leicester, the influential 1923 textbook
Thermodynamics and the Free Energy of Chemical Reactions by
Gilbert N. Lewis and Merle Randall led to the replacement of the term “affinity” by the term “free energy” in much of the English-speaking world.
History
Physical chemistry was one of the first branches of science to study the "theory of affinity". The name
affinitas was first used in the sense of chemical relation by German philosopher
Albertus Magnus near the year 1250. Later, those as
Robert Boyle, John Mayow,
Johann Glauber,
Isaac Newton, and Georg Stahl put forward ideas on elective affinity in attempts to explain how
heat is evolved during combustion reactions.
[1]The modern term chemical affinity is a somewhat modified variation of its eighteenth-century precursor "elective affinity" or elective attractions, a coinage of the Swedish chemist
Torbern Olof Bergman from his book
De attractionibus electivis .
Antoine Lavoisier, in his famed 1790
Elements of Chemistry, refers to Bergmann’s work and discusses the concept of elective affinities or attractions.
Geoffroy's 1718 affinity table
The first-ever
affinity table was published in 1718 by the French chemist
Étienne François Geoffroy. Geoffroy's name is best known in connection with these tables of "affinities" , which were first presented to the
French Academy in 1718 and 1720, as shown below:
These were lists, prepared by collating observations on the actions of substances one upon another, showing the varying degrees of affinity exhibited by analogous bodies for different reagents, and they retained their vogue for the rest of the century, until displaced by the profounder conceptions introduced by
Claude Berthollet.
Modern conceptions
In modern terms, we relate affinity to the phenomenon whereby certain atoms or molecules have the tendency to aggregate or bond. For example, in the 1919 book
Chemistry of Human Life physician George W. Carey states:
“Health depends on a proper amount of iron phosphate Fe32 in the blood, for the molecules of this salt have chemical affinity for oxygen and carry it to all parts of the organism.” In this antiquated context, chemical affinity is sometimes found synonymous with the term "magnetic attraction". Many writings, up until about 1925, also refer to a “law of chemical affinity”.
Thermodynamics
In 1923, the Belgian mathematician and physicist Théophile de Donder derived a relation between affinity and the Gibbs free energy of a
chemical reaction. Through a series of derivations, de Donder showed that if we consider a mixture of chemical species with the possibility of chemical reaction, it can be proved that the following relation holds:
With the writings of Théophile de Donder as precedent, Prigogine and Defay in
Chemical Thermodynamics defined chemical affinity as a function of the increments in uncompensated heat of reaction and reaction progress variable :
. .
This definition is useful for quantifying the factors responsible both for the state of equilibrium systems , and for changes of state of non-equilibrium systems .
Related
In 1809, based on the work of Bergmann, German scientist and philosopher
Johann Wolfgang von Goethe published the novella Elective Affinities which extended the chemical term “elective affinities” through storyline to human relationships, both intimate and political.
See also
References
- Partington, J.R. . A Short History of Chemistry. New York: Dover Publications, Inc. ISBN 0-486-65977-1
External links
- - 1920 Nobel Prize in Chemistry Presentation Speech by Gerard de Geer
