Question

A first order reaction has a rate constant of $15\times {10}^{-3}{s}^{-1}.$ How long will $5.0g$ of this reactant take reduce to $3.0g$?

• A. 34.07 seconds
• B. 61.09 seconds
• C. 24.07 seconds
• D. 14.09 seconds

Answer 1

The correct option is A 34.07 seconds

Applying first order kinetic equation,
$t=\frac{2.303}{k}lo{g}_{10}\frac{a}{a-x}$

Given : $k=15\times {10}^{-3}se{c}^{-1},a=5g,(a-x)=3g$

So, $t=\frac{2.303}{15\times {10}^{-3}}lo{g}_{10}\frac{5}{3}=34.07s$