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

Options

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

Answer

B

Explanation

Given, ` k = 10^(-2) s^(-1).`
Hence, `t_(1//2) = (0.693)/(k) = (0.693)/(10^(-2))` second
`20 g to 5 g ` takes two half lives
`( 20g to 10g to 5 g)`
Hence, `t = 2 xx (0.693)/(10^(-2)) = 138*6` second