* What happens: Silver tarnishes because it reacts with sulfur compounds in the air. This reaction forms silver sulfide (Ag₂S), a black compound that coats the silver surface.
* New substance: Silver sulfide is a completely different substance from pure silver. It has different chemical properties and a different appearance.
* Irreversible: The formation of silver sulfide is an irreversible process. You can't easily revert the silver sulfide back to pure silver without specific chemical treatments.
Key characteristics of a chemical change:
* Formation of new substances: The original substance is transformed into a new one with different properties.
* Irreversible: The change is usually difficult or impossible to reverse.
In contrast, physical changes only alter the appearance or form of a substance, not its chemical composition. For example, melting ice is a physical change because it's still water (H₂O) in both states.
