V5.7.3 Oscillating Reaction

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Animation of Experiment (GIF Format, 438 k)
Animation of Experiment (MPG Format, 346 k)

Chemical reactions do not always run in just one direction. The photos above show the process of a so-called "oscillating reaction." This is a case of a chemical reaction in which the concentration of a product over a given timespan periodically changes. The cause of this variation can be traced to the intermediate products, which influence the reaction speed of one or several reaction parts (backward coupling mechanism). This backward coupling mechanism, which leads to oscillations, can also be found poorly adjusted microphones and loudspeakers.

The reaction shown above is a variant of the so-called Belousov-Zhabotinskii reaction, which is composed of 18 elemental reactions. The laws govourning these reaction speeds are relatively complicated and will not be expanded upon here.

Literature (German): Angew. Chem. 90, 1-16 (1978), ChiuZ 7, 171 (1973)

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