In a first order reaction, the concentration of the reactant, decreases from 0.8 M to 0.4 M in 15 minutes. The time taken for the concentration to change from 0.1 M to 0.025 M is -

Options

A. 7.5 minutes
B. 15 minutes
C. 30 minutes
D. 60 minutes

Answer

C

Explanation

As the concentration of reactant decreases from 0.8 to 0.4 in 15 minutes, hence the `t_(1 // 2)` is 15 minutes. To fall the concentration from 0.1 to 0.025 we need two half lives as
`[A]=((1)/(2))^(n)` `[A]_(0)`, or `([A])/([A]_(0))=((1)/(2))^(n)`
`(0.1)/(0.025)=((1)/(2))^(n)`, n = 2, i.e., 30 minutes