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🔥 Reversible and Irreversible Changes

Some changes can be undone and some make brand-new materials forever. Learn to tell melting and dissolving from burning, rusting, and cooking.

3
lessons
~20 min
to learn
🔬 Science
subject
Ages 6–12
level
Start the course →

What you’ll learn

  1. Changes You Can UndoRecognise reversible changes such as melting, freezing, and dissolving, and know that no new material is made.Reversible changes can be undone so you get the same material back. Melting and freezing swap ice and water, and dissolving can be undone by evaporating. No new material appears in a reversible change.
  2. Changes You Can't UndoRecognise irreversible changes such as burning, rusting, and cooking, and know that they make new materials.Irreversible changes make brand-new materials that cannot turn back. Burning gives off smoke and ash, rusting needs iron, water, and air, and cooking changes food for good. None of these can be undone.
  3. Spot the DifferenceSort everyday changes into reversible and irreversible, using the clues of new materials.To tell the two apart, ask whether you can get the same material back. Reversible changes like melting can be undone; irreversible changes like burning and rusting make new materials, often with a new colour, smell, gas, heat, or light.

Questions this course answers

Why is melting an ice cube a reversible change?

Melting can be undone by freezing, and you get the same water and ice back, so it is reversible.

Which of these is a reversible change?

Dissolving is reversible because you can evaporate the water and get the sugar back. The others all make new materials.

What is the big clue that a change is irreversible?

An irreversible change makes a brand-new material, so there is no way to get the original back.

Three things are needed for iron to rust. Which is NOT one of them?

Rusting needs iron, water, and oxygen from the air. Sugar has nothing to do with it.

Why is frying an egg an irreversible change?

Cooking changes the egg into a new material for good — there is no way to turn a cooked egg back into a raw one.

Bubbles of a new gas, a colour change, or a new smell are signs of what kind of change?

New gases, new colours, and new smells are clues that a new material has been made — an irreversible change.

Grounded in trusted sources

  • Royal Society of Chemistry
  • BBC Bitesize
  • Britannica Kids
  • American Chemical Society

Every Wunder lesson is built from real, reputable sources — never invented.

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