Question

Consider the following reaction mechanism:

$\begin{array}{c}{\mathbf{\text{NO}}}_{\mathbf{2}}\mathbf{C}\mathbf{l}\mathbf{\to }{\mathbf{\text{NO}}}_{\mathbf{2}}\mathbf{}\mathbf{+}\mathbf{\text{Cl}}\\ {\mathbf{\text{Cl+H}}}_{\mathbf{2}}\mathbf{O}\mathbf{}\mathbf{\to }\mathbf{}\mathbf{\text{HCl+OH}}\\ {\mathbf{\text{OH+NO}}}_{\mathbf{2}}\mathbf{+}{\mathbf{N}}_{\mathbf{2}}\mathbf{\to }{\mathbf{\text{HNO}}}_{\mathbf{3}}\mathbf{+}{\mathbf{N}}_{\mathbf{2}}\end{array}$

(a) What is the molecularity of each elementary step?

(b) Write the overall equation for the reaction.

(c) Identify the reaction intermediate(s)

Short answer

a)The molecularity of the above steps are one, two, three.

b) The overall equation is ${\text{NO}}_2\text{Cl}+{\text{H}}_{2}O\to {\text{HCl+HNO}}_3......\left(1\right)$

C) The reaction intermediate are OH,NO_2,Cl and N_2.

Step-by-step solution

Step-1:   Molecularity of solution:

Consider the following reaction mechanism

$\begin{array}{l}{\text{NO}}_{2}Cl\to {\text{NO}}_2+Cl\\ {\text{Cl+H}}_{2}O\to \text{HCl+OH}\\ {\text{OH+NO}}_2+N_2\to {\text{HNO}}_3+N_2\end{array}$

In the above reaction the step-1 has only one reactent ,so it is called as unimolecular reaction.

Step-2 has two reactents participating in the reaction and so the order of the reaction is bimolecular reaction.

Step-3 has three reactents participating in the reaction and hence the rate of the reaction is trimolecular reaction.

Step-2: Overall equation of the reaction:

The overall reaction can be derived by adding all the above steps of the reaction and cancelling the common species on the either side of the steps.

$\begin{array}{l}N{O}_{2}Cl\to {\text{NO}}_2+Cl..................Step-1\\ {\text{Cl+H}}_{2}O\to \text{HCl+OH.}..............Step-2\\ {\text{OH+NO}}_2{\text{+N}}_2\to {\text{HNO}}_3+N_2.....Step-3\end{array}$

The overall equation obtained is given below

${\text{NO}}_2\text{Cl}+{\text{H}}_{2}O{\text{→HCl+HNO}}_3......\left(1\right)$

Step-3:  Reaction intermediate:

Reaction Intermediate can be defined as the chemical species which are formed during the course of a reaction, and are consumed in the series of steps, but they do not appear in the balanced reaction.

Example of intermediate species which are formed during the reaction steps are the following like OH,NO_2,Cl and N_2.

Therefore the reaction intermediates are OH,NO_2,Cl and N_2.