NEET | 2017Chemical Kinetics and Nuclear ChemistryHard

Question

A first order reaction has a specific reaction rate of 10-2 sec–-1. How much time will it take for 20g of the reactant to reduce to 5 g ?

Options

A.

18.6 sec

B.

346.5 sec

C.

693.0 sec

D.

238.6 sec

Solution

Half life of first order reaction t1/2 = 0.693K
=0.69310-2=69.3sec
Method-1

Total time = 2t1/2 = 2 × 69.3 = 138.6 sec
Method-2
t=2.303Klog[A]0[A]t
t=2.30310-2log205⇒t = 138.6 sec (Option 2)

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