Chemical oscillations1. Basic principles and examples

A chemical reaction is usually thought of as coming together of reactant molecules to form products. The concentrations of initial components (reactants) decrease, and concentrations of products increase until they reach a well defined state: the equilibrium. This process is accompanied by a decrease of the system free energy (compared at constant pressure and temperature), until it reaches a minimum in the equilibrium. Thus, it follows from the nature of the law of mass-action that every simple reaction approaches its equilibrium asymptotically, and the evolution of any physico-chemical system leads invariably to the steady state of maximum disorder in the universe. Normally, chemical systems approach equilibrium in a smooth, frequently exponential relaxation. Under special circumstances, however, coherent behavior such as sustained oscillations are observed and the oscillations of chemical origin have been present as long as life itself. Such reactions can be studied using mathematical models, the Lotka-Volterra model being the earliest and the simplest one.