A decomposition reaction occurs when a substance is broken down or split into two or more components.

They are divided into three categories. Thermal decomposition, electrolytic decomposition, and photo decomposition are all examples of decomposition reactions.
There are a plethora of breakdown reactions to consider.

When calcium carbonate is heated, it decomposes into calcium oxide and carbon dioxide.
The thermal breakdown is a heating-induced decomposition reaction.

Here is an illustration of that type of reaction:

2KClO₃(s) + Heat → 2KCl + 3O₂

In the reaction shown above, Potassium chromate decomposes into potassium chloride on heating along with the evolution of oxygen gas.