What is "chemical clock"

n. (context chemistry English) any mixture of compounds whose relative concentrations oscillate, and in which such change is marked by a visible rhythmic change in colour

A chemical clock or oscillating reaction is a complex mixture of reacting chemical compounds in which the concentration of one or more components exhibits periodic changes, or where sudden property changes occur after a predictable induction time. They are a class of reactions that serve as an example of non-equilibrium thermodynamics, resulting in the establishment of a nonlinear oscillator. The reactions are theoretically important in that they show that chemical reactions do not have to be dominated by equilibrium thermodynamic behavior.

In cases where one of the reagents has a visible color, crossing a concentration threshold can lead to an abrupt color change in a reproducible time lapse. Examples of clock reactions are the Belousov-Zhabotinsky reaction, the Briggs-Rauscher reaction, the Bray-Liebhafsky reaction and the iodine clock reaction. The concentration of products and reactants of oscillatory chemical systems can be approximated in terms of damped oscillations.