Half life of a reaction (t1/2): It is the time in which the concentration of a reactant is reduced to one half of its initial concentration. It is represented by t1/2.
Ø  Half Life of a Zero Order Reaction: For a zero order reaction, the integrated rate law is: 
k = [R0] – [R]            
            t
When t = t1/2, [R] = ½ [R0]
On substituting these values in the above equation,  
k = [R0] – ½ [R0]  
             t1/2

      
   t1/2 = [R0]
            2k

From above relation we can say Half life of a zero order reaction is directly proportional to the initial concentration of the reactants and inversely proportional to the rate constant.

Ø  Half Life of a First Order Reaction: For a first order reaction, the integrated rate law is: 



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