NEET Chemistry Chemical Kinetics Questions Solved


(a) A first order reaction takes 100 minutes for completion of 60% of the reaction. Find the time when 90% of the reaction will be completed.

(b)With the help of diagram explain the role of activated complex in a reaction.

(a) For the first order reaction,

     k=2.303tlog aa-x

When reaction is 60% complete

    x=60100a = 0.6a,

 t= 100 min-1

then k =2.303tlog aa-0.6a

k =2.303100log a0.4a

k =2.303100log 2.5        .....(1)

   t= ?, when reaction is 90% complete

  x = 0.9a

then k =2.303tlog aa-x

k =2.303tlog aa-0.9a

 k =2.303100log 10        .......(2)

Taking equations (1) and (2), we get 

2.303100log2.5 = 2.303tlog 10

 0.3979100=1t       t=1000.3979

 t= 251.31 minutes 

(b)  In order that the reactant may change into products ,they have to cross an energy barrier as shown in the diagram :

This diagram is obtained by plotting potential energy vs. reaction coordinate. It is believed that when the reactant molecules absorb energy, their bonds are loosened and new bonds are formed between them. The intermediate complex thus formed is called activated complex. It is unstable and immediately dissociates to form the stable products.


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