Question

Give an example of decomposition reaction. Describe an activity to illustrate such a reaction by heating.

Answer 1

A decomposition reaction is a reaction that breaks or decomposes the constituent reactant into 2 or more products upon the occurrence of the reaction. The occurrence of the reaction is usually due to the input of a huge energy in the form of heat, light and electricity, or in other words it is usually an endothermic reaction.

Complete Step by Step answer
As we know, a decomposition reaction is a type of chemical reaction in which a chemical compound breaks down into 2 or more chemical substances when heat, light or any other form of energy is supplied to the reactants or into the system where the chemical reaction occurs.
The reaction would be of the form,
$AB \to A + B$ where $AB$ is a chemical compound, which on supplying energy breaks down into simpler chemical substances, $A$ and $B$ .The simplest example of a chemical decomposition reaction is, the reaction that changes water into its constituting elements hydrogen and oxygen, by supplying energy in the form of electricity.
$2{H_2}O\left( l \right)\xrightarrow{{electricity}}2{H_2}\left( g \right) + {O_2}\left( g \right)$
Here we can see that electricity is being passed through liquid water to help it decompose into its constituting components hydrogen and oxygen. This reaction is a classic example of decomposition and is called electrolysis of water.
Decomposition can also occur by supplying heat to it, and this kind of decomposition is called thermal decomposition. An example of a thermal decomposition reaction is the formation of lead oxide, nitrogen dioxide and oxygen on heating lead nitrate.
This activity can be carried out using a test tube and Bunsen burner. Take a pinch of lead nitrate in the test tube and heat it over the flame from Bunsen burner. After heating for a few minutes, you can observe brown fumes, indicating the release of Nitrogen dioxide, while a brown residue of lead oxide is left in the test tube, and oxygen is released as a colour and odourless gas.
$2Pb{\left( {N{O_3}} \right)_2}(s)\xrightarrow{{heat}}2PbO\left( s \right) + 4N{O_2}\left( g \right) + {O_2}\left( g \right)$
Thus, the thermal decomposition of lead nitrate happens in the test tube.

Note
For a thermal decomposition reaction to occur you always need energy to be supplied to the reactant because the energy supplied is used to dissociate the bond between atoms. The energy can be of any form.