Question

The unit of rate constant $\left(k\right)$ for a zero order reaction will be:

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• A. $s^{-1}$
• B. $Lmo{l}^{-1}{s}^{-1}$
• C. $mol{L}^{-1}{s}^{-1}$
• D. $L^{2}mo{l}^{-2}{s}^{-1}$

Answer 1

The correct option is C $mol{L}^{-1}{s}^{-1}$

Generalized formula for the unit of rate constant $\left(k\right)$ for a $n^{th}$ order reaction.
Let ,
$A\to \text{Products}$
is a $n^{th}$ order reaction.
$\text{Rate}\left(R\right)=k[A{]}^n$

$\text{Units of}k=\frac{\text{Units of rate}}{\text{Units of}[A{]}^n}$

Since, rate is change of concentration w.r.t time
So, units of rate are $\frac{mol}{L.s}$

$\text{Units of}k=\frac{\frac{mol}{L.s}}{{\left(\frac{mol}{L}\right)}^n}$

$\text{Units of}k={\left(\frac{mol}{L}\right)}^{(1-n)}\times s^{-1}$

For a zero order reaction, $n=0$:
$\text{Units of}k={\left(\frac{mol}{L}\right)}^1\times s^{-1}=mol{L}^{-1}{s}^{-1}$