Question

37. Decomposition of (A) follows first order kinetics A +
products. Concentration of A, changes from 0.1 M
to 0.025 M in 1.381 minutes. Find the rate of the
reaction of A when concentration of A is 0.02 M.
(1) 2 x 10-2 M min-1
(2) 1.25 * 10-2 M min-1
(3) 0.693 x 10-3 M min-1
(4) 1 x 10-2 M min-1​

Answer 1

answer : option (1) 2 × 10^-2 M/min

explanation : initial concentration of A , $[A]_0$ = 0.1M

concentration of A after 1.381min, $[A]$ = 0.025M

it is mentioned that, decomposition of A is a first order reaction.

so, $k=\frac{2.303}{t}log\left(\frac{[A]_0}{[A]}\right)$

= 2.303/1.381 log(0.1/0.025)

= 2.303/1.381 × log4

≈ 1 sec^-1

now, rate of reaction when concentration of A is 0.02M, d[A]/dt = k[A]'

= 1 × 0.02

= 2 × 10^-2 M/min

so, rate of reaction of A is 2 × 10^-2 M/min