Irreversible Changes · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Irreversible changes: no going back

Science · Matter & Materials · ages 9-11
Name ______________________   Date ____________

  1. An irreversible change makes a new material that cannot easily change back.

    Circle one:   True   False

  2. A baked cake can be turned back into runny cake mixture.

    Circle one:   True   False

  3. When a piece of wood burns, what is the brand new material it leaves behind?

    • Sawdust
    • Warm water
    • Ash

  4. Which change is irreversible?

    • Melting ice into water
    • Burning a piece of wood
    • Freezing water into ice

  5. Which sign tells you an irreversible change might be happening?

    • The object gets bigger
    • Bubbles of gas appear
    • The object gets colder

  6. Sam bakes a cake. Which clue tells him the change was one-way?

    • A new material formed
    • The cake tin was washed
    • The kitchen stayed cool

  7. The four clues of an irreversible change are bubbles of gas, a colour change, heat given off, and a new material forming. Mia leaves an iron nail out in the rain. It turns orange, and flaky new rust forms on it. How many of the four clues does she see?

    Answer: ______________

  8. Which of these three changes is the one-way change?

    • Dissolving sugar in a cup of tea
    • Melting chocolate in the sun
    • Baking a cake

  9. Sara scrapes the black bits off her burnt toast and says she has turned it back into bread. What is wrong with her idea?

    • Scraping only takes the burnt bits away and does not turn the toast back into bread
    • Toast was never bread in the first place
    • Burnt toast turns back into bread if you wait

  10. Ben says he can pour the fizzing out of the bowl and get calm vinegar and dry bicarbonate of soda back. What is wrong with his idea?

    • Vinegar and bicarbonate of soda never fizz
    • The bowl is too small to pour from
    • Fizzing means a new gas formed, and you cannot turn the mixture back into what it was
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Irreversible changes: no going back W1-mt_rbPioPELM1-s1

  1. True · That's the definition. Once the new material forms, you can't easily undo it.
  2. False · Baking makes a new material. No cooling or stirring turns a cake back into mixture.
  3. Ash · Burning wood leaves ash, a new material. Ash can never turn back into wood.
  4. Burning a piece of wood · Burning wood makes ash and smoke, a new material. You can't turn ash back into wood.
  5. Bubbles of gas appear · Gas bubbles are one sign that a new substance is forming.
  6. A new material formed · The runny mixture turned into cake, a brand new material. A new material forming is one of the four clues.
  7. 2 · The colour change is one clue, and the new rust forming is another. That makes 2 clues.
  8. Baking a cake · Baking makes a new material. Dissolving and melting can both be undone.
  9. Scraping only takes the burnt bits away and does not turn the toast back into bread · Scraping moves the burnt part away. What is left is still toast, a new material.
  10. Fizzing means a new gas formed, and you cannot turn the mixture back into what it was · Once the new gas forms, the change is done. Pouring the mixture around cannot unmake a new material.
Worksheet · LightMySky