JEE Main · 2023 · 25 Jan 2023 · Shift 1 · Chemical Kinetics

For the first order reaction

A \to B

the half life is 30 min. The time taken for

75%

completion of the reaction is ______ min. (Nearest integer)

Given:

lo g 2 = 0.3010

lo g 3 = 0.4771

lo g 5 = 0.6989

Answer: 60

Solution

A first-order reaction consumes half of whatever remains in each successive half-life. After one half-life of

30

min half the reactant is left, and after a second half-life half of that again remains, so three-quarters of the original has reacted. Reaching

75%

completion therefore takes two half-lives, which is

2 \times 30 = 60

min.

JEE Main · 2023 · 25 Jan 2023 · Shift 1 · Integer answer