Physical changes
Change the shape, state or location — but the SUBSTANCE stays the same.
A physical change doesn't create new substances. The molecules are still the same; they're just rearranged. Examples:
- Melting ice → water (still H₂O).
- Cutting paper (same paper, just smaller).
- Dissolving salt in water (salt is still NaCl; you can recover it by evaporating).
- Stretching a rubber band.
Most physical changes are reversible: refreeze water, evaporate salt water, let the rubber band relax. The substance is unchanged at the end.
- No new substance.
- Usually reversible.
- Examples: melting, dissolving, cutting, stretching.