* Chemical Properties: Describe how a substance reacts with other substances. They involve changes in the composition of the substance.

* Physical Properties: Can be observed without changing the substance's chemical makeup.

When sodium reacts with water, it undergoes a chemical change:

* Sodium (Na) + Water (H2O) -> Sodium hydroxide (NaOH) + Hydrogen gas (H2)

The sodium atoms react with water molecules, forming new substances (sodium hydroxide and hydrogen gas). This change in composition is what makes it a chemical property.

The violence of the reaction is a result of the energy released during this chemical change.