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

Half life of a first order reaction
`t_(1//2) = (0.693)/(K) = (0.693)/(10^(-2)) = 69.3` sec
Method - 1

Total time = `2t_(1//2) = 2 xx 69.3 = 138.6` sec
Method-2
`t = (2.303)/(K)` log `([A]_(0))/([A]_(t))`
`t = (2.303)/(10^(-2)) "log" (20)/(5) implies t = 138.6` sec