Question

Identify the order of the reaction from the following rate constants respectively
a. $k=7.06\times {10}^{-3}{\text{mol}}^{-1}{\text{L s}}^{-1}$
b. $k=5.60\times {10}^{-5}{\text{s}}^{-1}$
c. $k=1.25\times {10}^{-2}{\text{mol L}}^{-1}{\text{s}}^{-1}$
d. $k=1.25\times {10}^{-2}{\text{mol}}^{-2}{\text{L}}^2{\text{s}}^{-1}$

• A. $0,1,2,3$
• B. $2,1,0,3$
• C. $3,1,0,2$
• D. $3,0,1,2$

Answer 1

The correct option is B $2,1,0,3$

Here we can identify the order of the reaction from the unit of the rate constants given.
We know, unit of rate constant $={\left[\frac{1}{\text{unit of concentration}}\right]}^{n-1}\times {\text{time}}^{-1}$
$={\left[\frac{\text{litre}}{\text{mol}}\right]}^{(n-1)}\times {\text{sec}}^{-1}$
Where, $n$ = order of the reaction

(a) $k=7.06\times {10}^{-3}{\text{mol}}^{-1}{\text{L s}}^{-1}$
So here, $n=2$ and hence it is a second order reaction.

(b) $k=5.60\times {10}^{-5}{\text{s}}^{-1}$
So here, $n=1$ and hence it is a first order reaction.

(c) $k=1.25\times {10}^{-2}{\text{mol L}}^{-1}{\text{s}}^{-1}$
So here, $n=0$ and hence it is a zero order reaction.

(d) $k=1.25\times {10}^{-2}{\text{mol}}^{-2}{\text{L}}^2{\text{s}}^{-1}$
So here, $n=3$ and hence it is a third order reaction.