A first order reaction has a specific reaction rate of `10^(-2) sec^(-1)`. How much time will it take for `20g` of the reactant to reduce to `5g` ?

Options

A. 138.6 sec
B. 346.5 sec
C. 693.0 sec
D. 238.6 sec

Answer

A

Explanation

`20 g overset((t_(1//2))_(1))rarr 10 g overset((t_(1//2))_(2))rarr 5g`
Thus, two half-lives are involved are reduce `20 g` of the reactant to `5g`
For first order reaction:
`t_(1//2) = (0.693)/(K) = (0.693)/(10^(-2) sec^(-1))`
`= 69.3 sec`.
Thus, total time required will be `2 xx t_(1//2) = 2 xx 69.3 sec`
`= 138.6 sec`.