Editing Chain reaction (section)

=== History ===
In 1913, the German chemist [[Max Bodenstein]] first put forth the idea of [[chemical]] chain reactions. If two molecules react, not only molecules of the final reaction products are formed, but also some unstable molecules which can further react with the parent molecules with a far larger probability than the initial reactants. (In the new reaction, further unstable molecules are formed besides the stable products, and so on.)

In 1918, [[Walther Nernst]] proposed that the [[photochemistry|photochemical]] reaction between [[hydrogen]] and [[chlorine]] is a chain reaction in order to explain what is known as the ''[[quantum yield]]'' phenomena. This means that one [[photon]] of light is responsible for the formation of as many as 10<sup>6</sup> molecules of the product [[HCl]]. Nernst suggested that the photon dissociates a Cl<sub>2</sub> molecule into two Cl atoms which each initiate a long chain of reaction steps forming HCl.<ref name=Laidler288>Laidler K.J., ''Chemical Kinetics'' (3rd ed., Harper & Row 1987) p.288-290  {{ISBN|0-06-043862-2}}</ref>

In 1923, Danish and Dutch scientists J. A. Christiansen and [[Hendrik Anthony Kramers]], in an analysis of the formation of polymers, pointed out that such a chain reaction need not start with a molecule excited by light, but could also start with two molecules colliding violently due to thermal energy as previously proposed for initiation of chemical reactions by [[Jacobus Henricus van 't Hoff|van' t Hoff]].<ref name=Nobel1956/>

Christiansen and Kramers also noted that if, in one link of the reaction chain, two or more unstable [[molecules]] are produced, the reaction chain would branch and grow. The result is in fact an exponential growth, thus giving rise to explosive increases in reaction rates, and indeed to chemical explosions themselves. This was the first proposal for the mechanism of chemical explosions.

A quantitative chain chemical reaction theory was created later on by Soviet physicist [[Nikolay Semyonov]] in 1934.<ref>{{cite web |url=http://www.marka-art.ru/catalogs/StampSeries.jsp?%26id%3D29264%26lang%3Den |title=Postal stamps series |access-date=2012-04-17 |url-status=dead |archive-url=https://web.archive.org/web/20090116032126/http://www.marka-art.ru/catalogs/StampSeries.jsp?&id=29264&lang=en |archive-date=2009-01-16 }}</ref> Semyonov shared the Nobel Prize in 1956 with Sir [[Cyril Norman Hinshelwood]], who independently developed many of the same quantitative concepts.<ref name=Nobel1956>http://nobelprize.org/nobel_prizes/chemistry/laureates/1956/press.html History of the chemical chain reaction from 1913 to the Nobel work recognized in 1956</ref>