Some changes can be undone: melted chocolate sets again, and salt can be recovered from salty water. Others are permanent: you can’t un-bake a cake or un-burn a log. At the Change Chamber, Year 5 scientists learn to tell the two apart.
What your child will learn
- Know that melting, freezing, evaporating and dissolving are reversible
- Know that burning, cooking and rusting are irreversible
- Spot signs that a new material has been made
- Explain how to reverse a simple change
Still the same stuff?
In a reversible change the material is still the same underneath: ice, water and steam are all water. In an irreversible change a new material is formed — ash and smoke from wood, or rust from iron — and there is no way back.
Clues to a permanent change
Look for fizzing or bubbles of gas, a change of colour, a new smell, or heat and light being given off. Vinegar on bicarbonate of soda fizzes because a new gas is being made.
Example questions
Here are a few questions like the ones in the first quest. Can you solve them?
1. Which change can be undone by cooling?
- Melting wax
- Burning wax
- Toasting bread
- Baking clay
Show answer
Answer: Melting wax. Melted wax hardens again as it cools.
2. True or false? Ice melting into water is a reversible change.
Show answer
Answer: True. Water can be frozen to make ice again.
3. Which of these is a reversible change?
🍫- Frying an egg
- Baking a cake
- Burning paper
- Melting chocolate
Show answer
Answer: Melting chocolate. Melted chocolate becomes solid again when it cools.
Tips for grown-ups
- Melt and re-set chocolate, then bake a biscuit — which change can you undo?
- Add vinegar to bicarbonate of soda and list the signs of a new material.
- Leave a damp iron nail and a dry one for a week and compare them.