Question

A first order reaction completes its 10% in 20 minutes, then the time required to complete its 19% is ____________.

Options

• 30 minutes

• 40 minutes

• 50 minutes

• 38 minutes

Answer 1

A first order reaction completes its 10% in 20 minutes, then the time required to complete its 19% is 40 minutes.

Explanation:

In first phase, k = `2.303/20 log  100/90` .......(i)

In second phase, k = `2.303/"t" log  100/81` ........(ii)

From eq. (i) and (ii)

`2.303/(20  "min") log  100/90 = 2.303/"t" log  100/81`

0.11515 × 0.0457 min⁻¹ = `2.303/"t" xx 0.0915`

t = `0.2107/(5.2623 xx 10^-3)` min

= 40.0 min