NEET Chemistry Chemical Kinetics Questions Solved

BOARD

(a) A reaction is second order in A and first order in B.

(i) Write the differential rate equation.

(ii) How is the rate affected on increasing the concentration of A three times?

(iii) How is the rate affected when the concentrations of both A and B are doubled?

(b) A first order reaction takes 40 minutes for 30% decomposition. Calculate t1/2 for this reaction (Given log 1.428 = 0.1548)

(a) (i) Differential rate equation :

             dxdt=K[A]2[B]

    (ii) When concentration of A is increased to three times, the rate of reaction becomes 9 times

                r=K[3A]2B         r=9KA2 i.e. =9 times 

    (iii)     r=K[2A]2[2B]       r=8KA2 i.e. =8 times

(b) Given :  Time, t = 40 minutes,   t1/2 =?

     Let a = 100,             x = 30% of 100 =30

Using the formula :

       t    =    2.303Klogaa-xor  40 =    2.303Klog100100-30or  K=    2.30340log10070or  K=    2.30340(log10 -log 7)or  K=    2.30340(1-0.8451)or  K= 2.30340×0.1549or  K=0.356740= 0.0089 min t1/2= 0.693K=0.6930.0089= 77.86 min

Difficulty Level: