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

Halflife for a first order reaction,
`t_(1 // 2)=(0.693)/(K)`
So, `t_(1 // 2)=(0.693)/(10^(-2))` sec
Also, for the reduction of 20 g or reactant to 5 g, two halflives will be required.
`:.` For 20 g of the reactant to reduce to 5g, time taken, `t=2 xx (0.693)/(10^(-2))` sec = 138.6 sec.