Question

The rate constant of a reaction is 0.01s^-1, how much time does it take for 2.4 mol L^-1 concentration of reactant reduced to 0.3 mol L^-1?

(a) 108.3s^-1

(b) 207.9s^-1

(c) 248.2s^-1

(d) 164.8s^-1

I got this question in examination.

Enquiry is from Chemical Kinetics in section Chemical Kinetics of Chemistry – Class 12

Answer 1

Correct option is (b) 207.9s^-1

For explanation I would say: Given,

K = 0.01s^-1

t1/2 = 0.693/0.01

t1/2 = 69.3s

[R] = [R]0/2^n

2^n = [R]0/[R]

2^n = 2.4/0.3

2^n = 8

n = 3 (number of half-lives)

For 1 half-life t1/2 = 69.3s

For 3 half-life 3t1/2 = 3 x 69.3s = 207.9s.