Belousov-Zhabotinskii reaction

A Belousov-Zhabotinski reaction, or BZ reaction, is one of a class of reactions that result in the establishment of a nonlinear chemical 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 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.

The discovery of the original phenomenology 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, and citric acid in dilute sulfuric acid, the ratio of concentration of the cerium(IV) and cerium(III) ions oscillated. He 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 editor of the journals to which he submitted his results.

Later, in 1961, a graduate student named A. M. Zhabotinski rediscovered this reaction sequence, however, the results of these men's work was still not widely dissemenated, and was not known in the west until a conference in Prague in 1968.

There are a number of BZ cocktails available in the chemical literature and on the web (http://www.zoo.co.uk/~z0001246/zhab). These reactions are usually carried out in petri dishes and result in the formation first of colored spots. These spots grow into a series of expanding concentric rings or perhaps expanding spirals. The colors disappear if the dishes are shaken, and then reappear. The waves continue until the reagents are consumed.