Here's a breakdown:

* One reactant: The reaction starts with a single substance (the reactant).

* Multiple products: The reactant breaks down into two or more different substances (the products).

* Energy input: Decomposition reactions usually require energy input to break the bonds in the reactant molecule. This energy can be in the form of heat, light, or electricity.

Examples:

* Electrolysis of water: Water (H₂O) is decomposed into hydrogen gas (H₂) and oxygen gas (O₂) by passing an electric current through it.

* Heating of calcium carbonate: Calcium carbonate (CaCO₃) decomposes into calcium oxide (CaO) and carbon dioxide gas (CO₂) when heated.

Key Points:

* Decomposition reactions are the opposite of synthesis reactions, where two or more substances combine to form a single compound.

* These reactions are common in many chemical processes, including the breakdown of food in our bodies and the production of metals from ores.