Year 5 Science: Irreversible changes and new materials
Part of the Year 5 Science reversible and irreversible changes chapter. Chapter overview · whole chapter on one page
Irreversible changes and new materials
Some changes make new materials. The new materials have different properties from the original ones. These changes are usually irreversible, which means they cannot be undone.
Examples include:
- burning, such as a candle burning, which makes ash, soot and gases;
- cooking an egg, which changes the egg so that it cannot become raw again;
- baking a cake, which makes new materials that are not the same as the mixture before it was cooked.
Key ideas
- Some changes make new materials, with different properties.
- Burning makes new materials, such as ash and gases.
- Cooking an egg is a change that cannot be undone.
- New materials usually cannot be changed back to the original materials.
Method. Think about whether the wax can be recovered.
- Think about the wax. The wax is changed into new materials, such as soot and gases.new materials
- Decide. So burning is not reversible, and the answer is no.no
- Write the answer. no
Check. New materials cannot easily be changed back. ✓
Method. Think about the change.
- Think about the egg. Cooking changes the egg, so it cannot become raw again.cannot become raw
- Decide. So the answer is no.no
- Write the answer. no
Check. Cooking is an irreversible change. ✓
Method. Read the picture and the story.
- Read the story. Ruby sees black soot on the glass after the candle has burned.black soot
- Name the material. The new material is soot.soot
- Write the answer. soot
Check. Soot is a new material made in burning. ✓
Watch out
Watch out: a change that makes a new material is usually irreversible, even if it looks like a small change. Do not say that burning or cooking can be undone.
Try it (with your teacher). Look at a cooked food and a raw food, with your teacher. Describe the colour, smell and texture of each. Then write whether the change from raw to cooked can be undone. Burning is never done by pupils. Watch any burning only as a demonstration, from a safe distance.
Exam tip
Grown-up tip. Ask: “Can the egg be raw again? Why not?” Keep this at a calm and factual level, and avoid any unsafe demonstration at home.
Exercise 7C Irreversible changes and new materials
Method. Read section 7.3.
- Read the description. Burning makes new materials, which cannot easily be changed back.new materials
- Decide. So the answer is no.no
- Write the answer. no
Check. Burning is an irreversible change. ✓
Method. Read section 7.3.
- Read the description. Cooking changes the egg so that it cannot become raw again.cannot become raw
- Decide. So the answer is no.no
- Write the answer. no
Check. The cooked egg cannot be undone. ✓
Method. Read the story in section 7.3.
- Read the story. There is black soot on the glass after the candle has burned.black soot
- Name the material. The new material is soot.soot
- Write the answer. soot
Check. Soot is made when a candle burns. ✓
Method. Read the key ideas in section 7.3.
- Read the key idea. Changes that make new materials are usually irreversible.usually irreversible
- Fill the gap. So the missing word is irreversible.irreversible
- Write the answer. irreversible
Check. Irreversible means it cannot be undone. ✓
Method. Read the key ideas in section 7.3.
- Read the key idea. A change that cannot be undone is irreversible.cannot be undone
- Fill the gap. So the missing word is irreversible.irreversible
- Write the answer. irreversible
Check. Irreversible changes cannot easily be reversed. ✓
Method. Read section 7.3.
- Read the description. Cooking an egg is an irreversible change.irreversible
- Decide. So the statement is false.false
- Write the answer. false
Check. A cooked egg cannot become raw again. ✓
Method. Read the picture.
- Read the picture. The picture has one arrow, from raw egg to cooked egg.one arrow
- Count the arrows back. There are no arrows from the cooked egg back to the raw egg.0
- Write the answer. 0
Check. No arrow goes back, so the change cannot be undone. ✓
Method. Read the list in section 7.3.
- Read the list. Burning makes ash, soot and gases.ash
- Name the change. So the change is burning.burning
- Write the answer. burning
Check. Burning is a change that makes new materials. ✓
Method. Read the list in section 7.3.
- Read the list. Baking a cake makes new materials that are not the same as the mixture.new materials
- Decide. So baking is not reversible, and the answer is no.no
- Write the answer. no
Check. A baked cake cannot be turned back into a mixture. ✓
Method. Read the story in section 7.3.
- Read the story. Black soot is left on the glass.black soot
- Name it. The new material is soot.soot
- Write the answer. soot
Check. Soot is a new material, made by burning. ✓
Method. Think about what burning does to the wax.
- Think about the wax. Burning changes the wax into new materials.new materials
- Write the reason. So the wax cannot easily be changed back.changed back
- Write the answer. Accept any sentence that says burning makes new materials, so the wax has changed and cannot be easily changed back.
Check. New materials are not usually reversible. ✓
Method. Think about the egg after cooking.
- Think about the egg. Cooking changes the egg.changes the egg
- Write the reason. So it cannot be undone, and it cannot become raw again.cannot be undone
- Write the answer. Accept any sentence that says cooking makes new materials in the egg, so the egg cannot become raw again.
Check. Cooking changes the material in a way that cannot be undone. ✓