Question

(a) Write two observations when lead nitrate is heated in a test tube.

(b) Name the type of reaction.

(c) Write the balanced chemical equation to represent the above reaction.

Answer 1

Decomposition reaction:

A chemical reaction in which one substance splits into two or more single substances is called a Decomposition reaction.

Example: When Calcium carbonate$\left({\mathrm{CaCO}}_3\right)$ is heated it decomposes into Calcium oxide$\left(\mathrm{CaO}\right)$ and Carbon dioxide$\left({\mathrm{CO}}_2\right)$.

${\mathrm{CaCO}}_3\left(\mathrm{s}\right)\stackrel{\mathrm{heat}}{\to }\mathrm{CaO}\left(\mathrm{s}\right)+{\mathrm{CO}}_2\left(\mathrm{g}\right)$

(a) When Lead nitrate$\left(\mathrm{Pb}{\left({\mathrm{NO}}_3\right)}_2\right)$ is heated in a test tube it decomposes into Lead oxide$\left(\mathrm{PbO}\right)$ and Nitrogen dioxide$\left({\mathrm{NO}}_2\right)$, Oxygen$\left({\mathrm{O}}_2\right)$ gases evolved from it. Thus it is an example of a Decomposition reaction.

Observations:

1. Due to the formation of Lead Oxide, it will turn into yellow colour.
2. Due to the evolution of Nitrogen dioxide and Oxygen gases evolution, reddish-brown fumes will appear.

(b) Thermal decomposition reaction:

A decomposition reaction that occurs under heating is called a Thermal decomposition reaction

Hence, this reaction of Lead nitrate takes place under heating, it is a Thermal decomposition reaction.

(c) The balanced chemical equation is written as,

$\mathbf{2}\mathbf{Pb}{\mathbf{\left(}{\mathbf{NO}}_{\mathbf{3}}\mathbf{\right)}}_{\mathbf{2}}\mathbf{\left(}\mathbf{s}\mathbf{\right)}\mathbf{}\stackrel{\mathbf{heat}}{\mathbf{\to }}\mathbf{}\mathbf{2}\mathbf{PbO}\mathbf{\left(}\mathbf{s}\mathbf{\right)}\mathbf{}\mathbf{+}\mathbf{}\mathbf{4}{\mathbf{NO}}_{\mathbf{2}}\mathbf{\left(}\mathbf{g}\mathbf{\right)}\mathbf{+}\mathbf{}{\mathbf{O}}_{\mathbf{2}}\mathbf{\left(}\mathbf{g}\mathbf{\right)}$