- Belousov-Zhabotinsky reaction
A Belousov-Zhabotinsky reaction, or BZ reaction, is one of a class of reactions that serve as a classical example of
non-equilibrium thermodynamics, resulting in the establishment of a nonlinearchemical oscillator. The only common element in these oscillating systems are the inclusion of bromine and an acid. The reactions are theoretically important in that they show that chemical reactions do not have to be dominated by equilibrium thermodynamic behavior. These reactions are far from equilibrium and remain so for a significant length of time. In this sense, they provide an interesting chemical model of nonequilibrium biological phenomena, and the mathematical model of the BZ reactions themselves are of theoretical interest.
An essential aspect of the BZ reaction is its so called "excitability"- under the influence of stimuli, patterns develop in what would otherwise be a perfectly quiescent medium. Some clock reactions such as Briggs-Rauscher and BZ using the chemical ruthenium bipyridyl as catalyst can be excited into self-organising activity through the influence of light.
The discovery of the phenomenon is credited to Boris Belousov. He noted, sometime in the 1950s (the dates change depending on source, but it ranges from 1951 to 1958), that in a mix of
potassium bromate, cerium(IV) sulfate, propanedioic acidand citric acidin dilute sulfuric acid, the ratio of concentration of the cerium(IV) and cerium(III) ions oscillated, causing the colour of the solution to oscillate between a yellow solution and a colorless solution. This is due to the cerium(IV) ions being reduced by propanedioic acid to cerium(III) ions, which are then oxidized back to cerium(IV) ions by bromate(V) ions.
Belousov made two attempts to publish his finding, but was rejected on the grounds that he could not explain his results to the satisfaction of the editors of the journals to which he submitted his results. His work was finally published in a less respectable, non-reviewed journal. [B. P. Belousov. Периодически действующая реакция и ее механизм. [A periodic reaction and its mechanism] . Сборник рефератов по радиационной медицине (Compilation of Abstracts on Radiation Medicine), 147:145, 1959.]
Later, in 1961, a graduate student named
A. M. Zhabotinskyrediscovered this reaction sequence; [A. M. Zhabotinsky. Периодический процесс окисления малоновой кислоты растворе (исследование кинетики реакции Белоусова). [Periodic processes of malonic acid oxidation in a liquid phase.] Биофизика [Biofizika] , 9:306–311, 1964.] however, the results of these men's work were still not widely disseminated, and was not known in the West until a conference in Praguein 1968.
There are a number of BZ cocktails available in the chemical literature and on the web.
Ferroin, a complex of phenanthrolineand ironis a common indicator. These reactions, if carried out in petri dishes, result in the formation first of colored spots. These spots grow into a series of expanding concentric rings or perhaps expanding spirals similar to the patterns generated by a cyclic cellular automaton. The colors disappear if the dishes are shaken, and then reappear. The waves continue until the reagents are consumed. The reaction can also be performed in a beaker using a magnetic stirrer.
Andrew Adamatzky, a computer scientist in the
University of the West of Englandreported on liquid logic gates using the BZ reaction. [Motoike I., Adamatzky A. Three-valued logic gates in reaction-diffusion excitable media. Chaos, Solitons & Fractals 24 (2005) 107-114. [http://uncomp.uwe.ac.uk/adamatzky] ]
* Pabian and Zarins, "Banded Agates; Origins and inclusions", University of Nebraska-Lincoln, Educational circular #12.
* [http://www.scholarpedia.org/article/Belousov-Zhabotinsky_reaction The Scholarpedia article on the Belousov-Zhabotinsky reaction]
* [http://staff.science.nus.edu.sg/~parwani/c1/node65.html The Belousov-Zhabotinski Reaction]
* [http://www.chem.leeds.ac.uk/chaos/pic_gal.html Gallery of BZ demonstrations]
* [http://online.redwoods.cc.ca.us/instruct/darnold/deproj/Sp98/Gabe/ The Belousov-Zhabotinsky Reaction]
* [http://www.ux.his.no/~ruoff/BZ_Phenomenology.html The Phenomenology of the Belousov-Zhabotinsky Reacton, with pictures]
* [http://youtube.com/watch?v=g3JbDybzYqk&feature=related Video of BZ reaction]
* [http://ed.augie.edu/~awaspaas/inorg/bz.pdf The Belousov-Zhabotinski Reaction] PDF file
* [http://technology.newscientist.com/channel/tech/dn13341-paper-cargo-surfs-chemical-waves.html?feedId=online-news_rss20 Paper cargo surfs chemical waves] - Oscillating chemical waves induced by BZ reactions can propel small objects, "New Scientist", 18 February 2008
* [http://hopf.chem.brandeis.edu/anatol.htm The home page of Anatol M. Zhabotinsky]
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