* Metal Rusting: Chemical Change Rusting is a chemical reaction between iron, oxygen, and water. The iron atoms bond with oxygen atoms to form iron oxide (rust), which is a different substance with different properties than iron.

* Silver Tarnishing: Chemical Change Tarnishing is a similar process to rusting, but it involves silver reacting with sulfur compounds in the air to form silver sulfide, a dark substance that coats the surface.

* Water Boiling: Physical Change Boiling water changes its state from liquid to gas (steam), but the chemical composition (H₂O) remains the same. The change is reversible – the steam can condense back into water.

* Paper Burning: Chemical Change Burning paper is a combustion reaction. The paper reacts with oxygen in the air, producing ash, carbon dioxide, and water. The paper is transformed into entirely new substances, and the change is not easily reversible.

Key Difference:

* Physical changes affect the form or appearance of a substance but don't change its chemical composition. They are often reversible.

* Chemical changes result in the formation of new substances with different chemical properties. They are often difficult or impossible to reverse.