* Physical properties can be observed without changing the chemical composition of a substance. Examples include color, density, melting point, and boiling point.
* Chemical properties describe how a substance reacts with other substances or under certain conditions. They involve the formation of new substances with different chemical compositions.
When sodium metal reacts with water, it undergoes a chemical reaction. This reaction produces sodium hydroxide (NaOH), hydrogen gas (H2), and releases heat:
2 Na (s) + 2 H2O (l) → 2 NaOH (aq) + H2 (g) + Heat
The explosion is caused by the rapid release of heat and the production of flammable hydrogen gas. This change in chemical composition and the formation of new substances are the hallmarks of a chemical property.
