* New Substance Formation: The green substance that forms on copper is a new compound called copper carbonate (CuCO3). It's formed by a reaction between copper, oxygen, and carbon dioxide in the air.
* Irreversible Change: The green patina cannot be easily reversed back into pure copper. It requires a chemical process to remove it.
* Change in Composition: The original copper metal has a different chemical composition than the green copper carbonate.
In contrast, a physical change would only alter the appearance or state of matter without creating a new substance. Examples include melting ice or crushing a rock.
