Question

When Lead nitrate is heated it decomposes with a cracking sound, a reddish brown gas is liberated and a solid residue is left in the test tube. Name the type of the reaction.

Answer 1

1. Thermal decomposition reaction

When compounds undergo a decomposition reaction due to the effect of heat or temperature of the system, it is known as a thermal decomposition reaction.

2. Heating of Lead nitrate

It is given that Lead nitrate $\left[\mathrm{Pb}{\left({\mathrm{NO}}_3\right)}_2\right]$ is heated in the test tube. It decomposes to give a solid residue, that is, Lead oxide $\left(\mathrm{PbO}\right)$ and a reddish-brown gas called Nitrogen dioxide $\left({\mathrm{NO}}_2\right)$ as products. It shows that the reaction is an example of a thermal decomposition reaction as Lead nitrate is the single reactant that undergoes decomposition.
The chemical reaction is given below.

$$\begin{gathered} 2\mathrm{Pb}{\left({\mathrm{NO}}_3\right)}_2\left(\mathrm{aq}\right)+\mathrm{heat}\to 2\mathrm{PbO}\left(\mathrm{s}\right)+\hspace{0.17em}2{\mathrm{NO}}_2\left(\mathrm{g}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right) \\ \left(\mathrm{Lead}\mathrm{nitrate}\right)\left(\mathrm{Lead}\mathrm{oxide}\right)\left(\mathrm{Nitrogen}\mathrm{dioxide}\right)\left(\mathrm{Oxygen}\right) \end{gathered}$$

Thus, the type of reaction is a thermal decomposition reaction.