Question

A first order reaction is 75% completed in 60 minutes, the time required for it's 50% completion is ____________.

Options

• 30 min

• 60 min

• 120 min

• 40 min

Answer 1

A first order reaction is 75% completed in 60 minutes, the time required for it's 50% completion is 30 min.

Explanation:

i. [A]₀ = 100, [A]_t = 100 − 75 = 25, t = 60 min

For first order reaction,

k = `2.303/"t" log_10  (["A"]_0)/(["A"]_"t")`

∴ k = `2.303/(60  "min") log_10  100/25`

k = `(2.303 xx 0.6020)/(60  "min")`

k = 0.0231 min⁻¹

ii. The time required for 50% completion of reaction is,

`"t"_(1//2) = 0.693/(0.0231  "min"^-1)` = 30 min