Physical Change:
* No new substance is formed. The molecules themselves remain the same.
* Often reversible. You can often get the original substance back.
* Changes in state of matter (solid, liquid, gas) are common. Examples: melting ice, boiling water, freezing water.
* Changes in appearance, shape, or size. Examples: cutting paper, crushing a can, bending a wire.
Chemical Change:
* A new substance is formed. The molecules rearrange and form new bonds.
* Usually irreversible. You can't easily get the original substances back.
* Often accompanied by observable changes:
* Color change: Rusting iron, burning wood.
* Gas production: Baking soda and vinegar reacting.
* Precipitate formation: Mixing solutions that form a solid.
* Heat or light release: Combustion, explosions.
* Odor change: Food spoiling.
Here are some examples to help illustrate:
* Physical change: Dissolving sugar in water. The sugar is still present, just spread out in the water. You can evaporate the water and get the sugar back.
* Chemical change: Burning wood. The wood reacts with oxygen, forming ash, carbon dioxide, and other gases. You can't get the wood back.
In short, if the fundamental composition of the substance changes, it's a chemical change. If it just changes its form or appearance, it's a physical change.
