* Physical properties are characteristics that can be observed or measured without changing the substance's chemical composition. Examples include color, melting point, density, etc.

* Chemical properties describe how a substance reacts with other substances or how it changes its composition.

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

* 2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g)

This reaction produces sodium hydroxide (NaOH) and hydrogen gas (H₂). The sodium metal is transformed into a new substance, and this transformation is a key indicator of a chemical change. The heat generated by the reaction is enough to ignite the hydrogen gas, causing the flame we observe.

In summary: The reaction of sodium with water involves a change in the chemical composition of the sodium, making it a chemical property.