Question

The half-life of a first order reaction is 6.0 hour. How long will it take for the concentration of reactant to decrease from 0.4 M to 0.12 M?

विकल्प

• 10.42 h

• 9.51 h

• 30.36 h

• 4.25 h

Answer 1

10.42 h

Explanation:

For first order reaction,

k = `0.693/"t"_(1//2) = 0.693/(6.0  "h")` = 0.1155 h⁻¹

Here, [A]₀ = 0.4 M, [A]_t = 0.12 M

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

= `2.303/(0.1155  "h"^-1) xx log_10  0.4/0.12`

= `2.303/0.1155 xx 0.5224`

∴ t = 10.42 h