* New substances are formed: Sodium (Na) reacts with water (H₂O) to produce sodium hydroxide (NaOH) and hydrogen gas (H₂). This is a clear indication of a chemical change, as the starting materials are transformed into entirely different substances.
* Energy is released: The reaction is exothermic, meaning it releases heat. The hydrogen gas produced often ignites, resulting in a flame. This energy release is another hallmark of a chemical change.
* Irreversible: The reaction is not easily reversed. You can't easily get sodium and water back from the sodium hydroxide and hydrogen gas produced.
The reaction:
2 Na (s) + 2 H₂O (l) → 2 NaOH (aq) + H₂ (g)
In summary: The reaction of sodium with water involves the formation of new substances, the release of energy, and is essentially irreversible, all strong indicators of a chemical change.
