NEET Chemistry Chemical Kinetics Questions Solved

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(q) A first order reaction is 15% completed in 20 minutes. How long will it take to complete 60% of the reaction?

a. 112.8min

b.120.7 min

c.100.4 min

d.140.7min

 For the first order reaction

     K =2.303tlog aa-x

First case: a = 100, x = 15, time, t = 20 minutes

(a-x) = 100 - 15 = 85

t15% = 2.303Klog 10085

 20 = 2.303Klog 10085         ........(1)

Second case : a=100, x=60,  time,t60%= ?

(a-x) = 100 - 60 = 40

t60% = 2.303Klog 10040         .........(2)

Dividing equation (2) by (1), we get

t60%20=log10040log10085=log100-log40log100-log85

        = 2.000-1.60212.0000-1.9294

t60%20=0.39790.0706=5.64t60% = 20 ×5.64 =112.8 minutes

 

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