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Summaries · Grade 4 Natural Sciences › Reversible and irreversible changes
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Reversible and irreversible changes

Changes you can reverse, and changes that make something new. Read one part at a time and tap “I know this”. Then test yourself in the quiz.

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Two kinds of change

ReversibleIrreversible
Water freezes into iceA cake is baked
Butter melts in a panAn egg is fried
Chocolate sets in the fridgeWood burns to ash
Dew forms on the grassIron rusts
Salt dissolves in waterMilk goes sour
Sand and water mix (filter it out again)Clay is baked into a pot
Rule

Ask yourself: is there a new substance? Yes = irreversible. No, just another form = reversible.

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In the kitchen

Melted butter can set again, but a baked cake never becomes batter again.
Melted butter can set again, but a baked cake never becomes batter again.

Folding paper is mostly reversible (unfold it), but cutting it is not: it does not become one sheet again.

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Why is it useful?

If you know whether a change is reversible, you know whether you can get the substance back. A change where the substance stays the same is called a physical change.

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Remember this and test yourself

Remember this: your summary
  • A reversible change can change back to what it was.
  • Melting, freezing, evaporating, condensing and dissolving are reversible.
  • An irreversible change makes a new substance: burning, baking, rusting, going sour.
  • Get salt back from salt water by letting the water evaporate.
  • Glass can be recycled (melting is reversible), but a burnt log cannot.

Write these points in your book. Read them again the night before the test.

Memory trick

Can you un-do it? Ice ↔ water: yes. Cake → batter: never. Something new made = irreversible.

Flash cards · Tap to turn over

Important words

First say what the word means, then turn the card over.

Test yourself · Part 2

True or false?

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