Melting, freezing, dissolving, evaporating — you can get the original back. Ice → water → ice.
Burning, cooking, rusting, mixing some substances — a NEW material forms and can't change back.
Learn the Difference
1Reversible: same material, new form.
Melting chocolate, dissolving salt, freezing water — cool or evaporate and you recover the original.
2Irreversible: a new material.
Burning wood makes ash and smoke; cooking an egg changes it permanently; iron rusts. You can’t get the original back.
3Some mixtures react.
Mixing bicarbonate of soda and vinegar fizzes — a new gas forms. That fizzing signals an irreversible change.
Worked Example
Sort these: melting butter, frying an egg, dissolving sugar, burning toast.
Watch Out! Common Mistakes
It’s still there! Dissolved sugar spreads through the water invisibly. Evaporate the water and the sugar returns — a reversible change.
Not melting! Melting is reversible (re-freeze it). But cooking and burning ARE irreversible — the difference is whether a new material forms.
Watch for clues! Colour change, fizzing, a new smell or heat/light given off usually mean an irreversible change has made something new.
⬇ Cheat Sheet
- Reversible: melt, freeze, dissolve, evaporate — get the original back.
- Irreversible: burn, cook, rust, mix-and-react — a new material forms.
- Dissolving is reversible (evaporate to recover the solid).
- Signs of new material: colour change, fizzing, new smell, heat/light.
📖 Continue Your Journey
Quick summary
- Reversible changes recover the original: melting, freezing, dissolving, evaporating.
- Irreversible changes make a new material: burning, cooking, rusting.
- Dissolving is reversible — evaporate the water to get the solid back.
- New colour, fizzing, a new smell or heat/light signal an irreversible change.
Frequently asked questions
What is the difference between reversible and irreversible changes?
Reversible changes can be undone to recover the original material (melting, dissolving); irreversible changes create a new material that can't change back (burning, cooking).
Is dissolving reversible?
Yes — dissolved sugar or salt is still there, spread through the water. Evaporating the water brings the solid back.
How can you tell a new material has formed?
Look for a colour change, fizzing (a new gas), a new smell, or heat and light being given off — these signal an irreversible change.
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