(1) Definition :
Zero order reaction : A reaction in which the rate of the reaction does not depend on the concentration of any reactant taking part in the reaction is called zero order reaction.
(2) Explanation :
For example,
Consider photochemical reaction between H2 and Cl2 gases.
In this the rate of the reaction remains constant throughout the progress of the reaction, even if the concentrations of the reactants decrease with time, until the reactant has reacted entirely.
Hence, by the rate law,
R = k [H2]° [Cl2]° = k (constant).
