NEET Chemistry Chemical Kinetics Questions Solved

BOARD

(a) The decomposition of A into products has a value of K as 4.5 ×10s-1 at 10 C and energy of activation 60 KJ mol-1. At what temperature would K be 1.5 × 104 s-1?

(b)  (i) If half life period of a first order reaction is x and 3/4th life period of the same reaction is y, how are x and y related to each other ?

   (ii) In some cases it is found that a large number  of colloiding molecules have energy more than threshold energy, yet the reaction is slow, Why? 

(a) given : K1 = 4.5 × 103 s-1,

                T1 = 10K + 273K =283K

                K2 = 1.5 × 104 s-1,     T2 =?

               Ea = 60 KJ mol-1

 Using formula :

             log :    K2K1=Ea2.303 RT2-T1T1T2                      log 1.5×1044.5×103=60000 J mol-12.303 ×8.314 JK-1 mol-1T2-283283T2                 log 3.333 =3133.63 T2 -283283 T2                 0.52283133.63=T2-283283 T2                   0.0472 T2 = T2 - 283                  0.9528 T2 =283                   T2 =2830.9528 =297 K

  Temperatue, Twill be =297 - 273

                                       =24C

(b) (i) t1/2 =0.693K   (For first order reaction)

         t3/4 =K           t3/4 =1.3864K

According to condition

(The value 1.3864 is double of 0.693)

From the above equation it is clear that 

t3/4 =2t1/2                       y=2x

(ii) It is due to improper orientation of the colloiding molecules at the time of collision.

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