Single elective affinity


A cartoon depiction of divorce as a single displacement reaction (aka substation reaction or single elective affinity). [2]

A cartoon depiction of divorce as a single displacement reaction (aka substation reaction or single elective affinity). [2]

In chemistry, a single elective affinity or "single displacement reaction" (modern) is a reaction or affinity reaction, involving two affinities, in which one composition, consisting of two principles, is destroyed and at the same time a new compound is formed. [1]

Bergman

See main: EA|IAD: Reaction decipherment;

The following, to given example of single elective affinity, shows Swedish chemist Torbern Bergman's reaction #20 (see: Bergman reaction diagrams), in his own words, the "decomposition of calcareous hepar by vitriolic acid", as re-shown below:

The "+" sign here seems to indicate "with the addition of" [species indicated]; a reaction which, in words, is such that the calcareous hepar,

( $CaS \,$ )

	( $CaS \,$ )

described such that it has its "proximate principles [are] united", which are calcareous earth (calcium oxide, CaO) and sulphur (S):

( $CaO \,$ )
and ( $S \,$ )

	( $CaO \,$ )	and		( $S \,$ )

is decomposed [reacts with] vitriolic acid (sulfuric acid, H2SO4):

( $H_2 SO_4 \,$ )

	( $H_2 SO_4 \,$ )

in water, ∇ (H20), indicating that “the three surrounding bodies freely exercise their attractive powers in it”, to form gypsum and elemental sulphur:

( $CaSO_4 \,$ )
and ( $S \,$ )

	( $CaSO_4 \,$ )	and		( $S \,$ )

The separation of the signs of calcareous earth and hepar inside the vertical bracket { represents breaking of the combination of these two “proximate principles” by the action of the vitriolic acid, which “attracts calcareous earth more strongly than sulphur does.” The signs of the calcareous earth and vitriolic acid are placed side by side above a complete horizontal bracket—the indication that a new combination—the point of which is turned downwards to imitate that the new compound (vitriolated calcareous earth or gypsum) is precipitated. The fact that sulphur, which is the other product of the reaction, also precipitates, is indicated by turning downwards the point of the lower horizontal half bracket. [12] In modern terms, calcium sulfide CaS is decomposed by sulfuric acid H2SO4 in water calcium sulfate CaSO4, which precipitates (down full-bracket) and to produce elemental sulfur S which precipitates (downward half-bracket); which, neglecting intermediates, would be written as:

This reaction, of course, is an example of a single elective affinity (reaction).

References
1. Henry, William. (1831). The Elements of Experimental Chemistry, Volume 1 (Single elective affinity, pgs. 183-85; Double elective affinity, pgs. 185-86; ch. 2: Of Chemical Affinity, pgs. 37-; section: IV: Of Elective Affinity, pgs. 61-; section VI: Of the Estimation of the Forces of Affinity, pgs. 68-; section VII: Of Complex Affinity, pgs. 70-). D. Desilver.
2. Jarape. (year), “Substitution Reaction”, JarpeScienceCartoons.Blogspot.com.

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