Here's a breakdown:

* Pure substance: A substance made up of only one type of molecule or atom. Examples include water (H₂O), sugar (C₁₂H₂₂O₁₁), and pure gold (Au).

* Broken down: The chemical bonds within the substance are broken.

* Two or more substances: The original substance is transformed into new substances with different chemical compositions.

* Chemical reaction: This involves the rearrangement of atoms and the formation of new bonds.

Examples of Chemical Decomposition Reactions:

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

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

* Burning wood: Wood (a complex mixture of organic compounds) is decomposed into carbon dioxide (CO₂), water (H₂O), and other products when it burns.