* Physical Change: A change in the form or appearance of a substance, but not its chemical composition. Examples: melting ice, cutting paper.

* Chemical Change: A change where a new substance is formed with different properties. Examples: burning wood, rusting iron.

When copper turns green, it's undergoing a chemical reaction called corrosion. Here's what happens:

1. Exposure to air and water: Copper reacts with oxygen and water vapor in the air.

2. Formation of copper carbonate: The reaction forms a green layer of copper carbonate (CuCO3) and copper hydroxide (Cu(OH)2).

3. New substance: The green patina is a new substance with different properties than the original copper.

Since a new substance is formed, this is a chemical change.