Reversible response

A reversible reaction is understood to be a chemical reaction which is reversible ( foreign word derived from the Latin reverti = to reverse for reversible ). An example of a reversible reaction is the dimerization of cyclopentadiene , which takes place rapidly at room temperature by means of a Diels-Alder reaction :

When the temperature is increased, the reverse reaction, a retro-Diels-Alder reaction, takes place in which the monomer is reformed , which can then be removed from the reaction mixture by distillation.

In almost every reversible reaction, an equilibrium is established in the mixture between reactants (outdated: starting materials ) and products .

Irreversible reaction

The opposite of a reversible reaction is an irreversible reaction (from Latin in = un ... and revertere = to reverse) which is irreversible in only one direction and in which no equilibrium can be established. An example of an irreversible reaction is the burning of ethanol:

${\displaystyle \mathrm {H_{3}C{-}CH_{2}OH+\ 3\ O_{2}\longrightarrow 2\ CO_{2}+3\ H_{2}O} }$

history

The concept of the reversible reaction was established by Claude Louis Berthollet in 1803 after observing sodium carbonate crystals forming on the edges of a salt lake in Egypt :

${\displaystyle \mathrm {2\ NaCl+CaCO_{3}\longrightarrow Na_{2}CO_{3}\downarrow +CaCl_{2}} }$

This was the reverse reaction to a reaction he already knew from his laboratory:

${\displaystyle \mathrm {CaCl_{2}+Na_{2}CO_{3}\longrightarrow CaCO_{3}\downarrow +2\ NaCl} }$

Until then, it was assumed that chemical reactions only ever proceed in one direction. Berthollet concluded that the high excess of salt in the lake shifted the reaction in the opposite direction to the formation of sodium carbonate.

${\displaystyle \mathrm {CaCl_{2}+Na_{2}CO_{3}\ \rightleftharpoons \ CaCO_{3}+2\ NaCl} }$

literature

• A. Hadener, H. Kaufmann: Fundamentals of general and inorganic chemistry . Birkhäuser Verlag, Basel, 2006, ISBN 3-7643-7041-6 ( page 100 in the Google book search).

Individual evidence

1. ↑ Entry on reversible. In: Römpp Online . Georg Thieme Verlag, accessed on January 10, 2012.
2. ↑ Hans Peter Latscha, Uli Katzmeier, Alfons Klein: Organic Chemistry Chemistry Basic Knowledge II . Springer Verlag, 2008, ISBN 978-3-540-77106-7 ( pages 83-84 in the Google book search).
3. ↑ Entry on irreversible. In: Römpp Online . Georg Thieme Verlag, accessed on January 10, 2012.
4. ↑ How did Napoleon Bonaparte help discover reversible reactions? . Chem ₁ General Chemistry Virtual Textbook: Chemical Equilibrium Introduction: reactions that go both ways.
5. ^ Claude-Louis Berthollet: Essai de statique chimique , Paris, 1803. (Google books)