Chemical oscillations are necessary to drive the beating of the heart, the glycolytic cycle in our body, to maintain the concentrations of metabolytes and other hormones in the body and for several other processes in nature. In oscillatory chemical reactions, the concentrations of reactants and products vary periodically in time and/or space. The iodine clock reaction is a famous example. A few well known mechanisms for chemical oscillations are :
a) The Lotka - Volterra mechanism :
A + X 2X
X + Y 2 Y
(30.26)
Y B
b) The Brusselator mechanism :
A X
2 X + Y 3 X
B + X Y + C
(30.27)
X D
Here the concentrations of only X and Y vary and A and B are held at fixed concentrations.
c) The oreganator mechanism :
A + Y X
X + Y C
B + X 2X + Z
(30.28)
2 X D
Z Y
Here, X = HBrO2, Y = Br - and Z = 2Ce 4+. The concentrations of A, B, C and D are held fixed.
These reactions have generated a lot of interest. These reactions are far removed from equilibrium; they involve autocatalytic steps ( such as A + X 2X, with the reactants regenerating themselves) and the reacting system must be able to exist in two steady states (otherwise, the system will end up in the minimum free energy state of thermal equilibrium).
In the iodine clock reaction, the decomposition of H2O2 is catalysed by IO3-/ I2. The production of O2 is discontinuous and proceeds in bursts leading to the oscillations in the concentrations of I2.
2X 
