Question

A first order reaction has a specific reaction rate ${10}^{-2}{\text{sec}}^{-1}$. How much time will it take for $20\text{g}$ of the reactant to reduce to $5\text{g}$?

• A. $138.6\text{sec}$
• B. $346.5\text{sec}$
• C. $693.0\text{sec}$
• D. $238.6\text{sec}$

Answer 1

The correct option is A $138.6\text{sec}$

$t=\frac{2.30}{k}log\frac{a}{a-x}$
$=\frac{2.303}{{10}^{-2}}log\frac{20}{5}$
$=\frac{2.303\times 0.6}{{10}^{-2}}$
$=138.6\text{sec}$