Chapter 16, Problem 79A

Interpretation Introduction

Interpretation:

To determine the overall reaction for the decomposition of nitryl chloride $\left({\text{NO}}_{\text{2}}\text{Cl}\right)$ and determine any intermediates in the reaction sequence, and explain why they are called intermediates.

Concept introduction:

In a chemical reaction, the reactants are written on the left side of the equation and the product is written on the right side.

The average rate of a reaction can be given by the formula,

Average reaction rate $\text{=}-\frac{\text{Δ}\left[\text{reactant}\right]}{\text{Δt}}$

Here, $\text{Δ}\left[\text{reactant}\right]$ = change in the concentration of the reactant

Answer to Problem 79A

The overall reaction for the decomposition of nitryl chloride $\left({\text{NO}}_{\text{2}}\text{Cl}\right)$ is ${\text{2NO}}_{\text{2}}\text{Cl}\left(\text{g}\right)\to 2{\text{NO}}_{\text{2}}\text{(g)}\text{+}{\text{Cl}}_{\text{2}}\left(\text{g}\right)$. In this reaction, since, $\text{Cl}\left(\text{g}\right)$ is produce during the first step but is consumed during the step, hence, the intermediate in this reaction is $\text{Cl}\left(\text{g}\right)$

Explanation of Solution

Given, the following two step mechanism for the decomposition of $\left({\text{NO}}_{\text{2}}\text{Cl}\right)$

$\begin{array}{l}\text{Step}\text{1:}{\text{NO}}_{\text{2}}\text{Cl}\left(\text{g}\right)\to {\text{NO}}_{\text{2}}\text{(g)}\text{+}\text{Cl}\left(\text{g}\right)\\ \text{Step}\text{2:}{\text{NO}}_{\text{2}}\text{Cl}\left(\text{g}\right)\text{+}\text{Cl}\left(\text{g}\right)\to {\text{NO}}_{\text{2}}\text{(g)}\text{+}{\text{Cl}}_{\text{2}}\left(\text{g}\right)\end{array}$

Since, the reaction has two elementary reactions hence the overall reaction is a complex reaction.

Adding the two elementary steps we find out the overall reaction.

$\begin{array}{l}\underset{\_}{\begin{array}{l}\text{Step}\text{1:}{\text{NO}}_{\text{2}}\text{Cl}\left(\text{g}\right)\to {\text{NO}}_{\text{2}}\text{(g)}\text{+}\text{Cl}\left(\text{g}\right)\\ \text{Step}\text{2:}{\text{NO}}_{\text{2}}\text{Cl}\left(\text{g}\right)\text{+}\text{Cl}\left(\text{g}\right)\to {\text{NO}}_{\text{2}}\text{(g)}\text{+}{\text{Cl}}_{\text{2}}\left(\text{g}\right)\end{array}}\\ {\text{ 2NO}}_{\text{2}}\text{Cl}\left(\text{g}\right)\to 2{\text{NO}}_{\text{2}}\text{(g)}\text{+}{\text{Cl}}_{\text{2}}\left(\text{g}\right)\end{array}$

In this reaction, $\text{Cl}\left(\text{g}\right)$ is the intermediate that appears on both the sides in the net reaction, so this term cancels out.

So, the overall reaction is ${\text{2NO}}_{\text{2}}\text{Cl}\left(\text{g}\right)\to 2{\text{NO}}_{\text{2}}\text{(g)}\text{+}{\text{Cl}}_{\text{2}}\left(\text{g}\right)$

Conclusion

The overall reaction is ${\text{2NO}}_{\text{2}}\text{Cl}\left(\text{g}\right)\to 2{\text{NO}}_{\text{2}}\text{(g)}\text{+}{\text{Cl}}_{\text{2}}\left(\text{g}\right)$ and the intermediate in this reaction is $\text{Cl}\left(\text{g}\right)$.