Question

The experimental data for the reaction $2NO\left(g\right)+C{l}_2\left(g\right)\to 2NOCl\left(g\right)$ are given below:

Expt	$\left[C{l}_2\right]$	[NO]	Initial rate
1	0.020	0.010	$2.4\times {10}^{-4}$
2	0.020	0.030	$2.16\times {10}^{-3}$
3	0.040	0.030	$4.32\times {10}^{-3}$

The order of the reaction is:

• A. 1
• B. 2
• C. 3
• D. 0

Answer 1

The correct option is C 3

The rate law expression is $r=k\left[C{l}_2{]}^m\right[NO{]}^n$.

From experiments (1) and (2),
$\frac{2.16\times {10}^{-3}}{2.4\times {10}^{-4}}=\frac{k\left[0.020{]}^m\right[0.030{]}^n}{k\left[0.020{]}^m\right[0.010{]}^n}$
Hence, $n=2$.

From experiments (2) and (3),
$\frac{2.16\times {10}^{-3}}{4.32\times {10}^{-3}}=\frac{k\left[0.020{]}^m\right[0.030{]}^n}{k\left[0.040{]}^m\right[0.030{]}^n}$
Hence, $m=1$.

Thus, the order of the reaction is $m+n=1+2=3$.