Examples of physical changes
A physical change alters the form, size, shape or state of a substance without turning it into a new substance. Melting, freezing, boiling, dissolving, cutting and bending are all physical changes. The chemical composition stays the same, and many physical changes can be reversed.
- Ice melting — solid water becomes liquid water, but it is still H₂O.
- Water boiling — liquid water turns into water vapor (steam).
- Water freezing — liquid water turns into solid ice in the freezer.
- Steam condensing on a cold mirror — water vapor turns back into liquid droplets.
- Dry ice subliming — solid carbon dioxide turns straight into a gas without melting first.
- Frost forming on a window — water vapor turns directly into ice crystals (deposition).
- A puddle drying up — liquid water evaporates into the air.
- Sugar dissolving in water — the sugar spreads out but is still sugar, and evaporating the water leaves it behind.
- Salt dissolving in water — the salt can be recovered by evaporating the water.
- Butter melting in a warm pan — it changes from solid to liquid and firms up again when cooled.
- Candle wax hardening — melted wax cools and becomes solid again.
- Cutting paper — the pieces are smaller, but they are still paper.
- Crushing an aluminum can — its shape changes, not the metal it is made of.
- Breaking a glass — the broken pieces are still glass.
- Hammering metal into a thin sheet — metals are malleable and change shape without changing composition.
- Stretching a rubber band — it changes shape and springs back.
- Grinding coffee beans — large pieces become small pieces of the same material.
- Magnetizing an iron nail — rubbing it with a magnet lines up its magnetic domains, but no new substance forms.
- Mixing sand and iron filings — the two can be separated again with a magnet.
- Shaping wet clay — only its shape changes, although firing it in a kiln is a chemical change.
Physical or chemical change?
To decide, ask whether a new substance has formed. Melting ice still gives you water, so it is a physical change, while burning paper produces ash, smoke and gases, so it is a chemical change. Many physical changes are easy to reverse: you can refreeze water or evaporate salt water to get the salt back.
Be careful with clues. Bubbles, a temperature change or a new color can also appear in physical changes, as when water boils or a metal glows red-hot. And not every physical change is easy to undo: a broken glass is still glass, even though you cannot simply put it back together.