What is a chemical change? Give examples.

A chemical change produces new substances with properties entirely different from the originals, and is generally irreversible.

Indicators:

• Change in colour, evolution of gas, formation of precipitate, temperature change, change in smell.

Examples:

• Burning of wood → ash and smoke (irreversible)
• Rusting of iron → Fe₂O₃ forms
• Digestion of food → complex molecules broken down
• Cooking an egg → proteins denature (irreversible)

A chemical change produces entirely new substances with different properties and is usually irreversible.