Chemistry - Chemical Kinetics Question with Solution | TestHub

The rate law for a first order reaction is given by:

$\text{Rate}=k[A]$

The unit of rate of reaction is ${\text{mol dm}}^{-3}{\text{ s}}^{-1}$ and the unit of concentration $[A]$ is ${\text{mol dm}}^{-3}$.

Substituting these units into the rate law equation:

${\text{mol dm}}^{-3}{\text{ s}}^{-1}=k\times {\text{mol dm}}^{-3}$

$k=\frac{{\text{mol dm}}^{-3}{\text{ s}}^{-1}}{{\text{mol dm}}^{-3}}$

$k={\text{s}}^{-1}$

Thus, the unit of the rate constant for a first order reaction is ${\text{s}}^{-1}$.

Answer: ${\text{s}}^{-1}$