Science // Matter & Materials

Reversible Changes

Demonstrate that dissolving, mixing, and changes of state are reversible changes where no new materials are formed

Ages
9 to 10
Type
Concept
Builds on
3 topics
Leads to
3 topics
Standards
1 code

Quick check

Can the learner explain that melting chocolate or dissolving sugar can be undone — you can get the original material back — because these are reversible changes?

Ask this to see whether the topic is secure.

Topic // Mastery

What mastery looks like

What a learner can do once this topic is secure.
  • Define a reversible change as one where the original materials can be recovered
  • Give at least three examples of reversible changes: melting, freezing, dissolving, evaporating
  • Explain how to reverse each example (e.g. freeze melted chocolate, evaporate a solution)

Topic // Map

Where this fits

What to learn first and what this topic opens up, with the reason for each link. Required links come first.
  • RequiredMust come first
  • HelpfulHelps, but not essential

Before this

3 topics
  • Heating & Cooling ChangesRequired

    Matter & Materials // Ages 7 to 9

    Must understand state changes before categorising them as reversible

  • Dissolving & SolutionsRequired

    Matter & Materials // Ages 9 to 10

    Must understand dissolving before demonstrating it is reversible

  • Changes & Separation VocabularyHelpful

    Matter & Materials // Ages 7 to 9

    Describing dissolving and changes of state as reversible requires the vocabulary from the process terms node

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Reversible Changes

Ages 9 to 10 // Concept

Leads to

3 topics
  • Irreversible ChangesRequired

    Matter & Materials // Ages 9 to 11

    Must understand reversible changes before contrasting with irreversible ones

  • Conservation of MassRequired

    Matter & Materials // Ages 10 to 11

    Must understand reversible changes before investigating conservation of mass during changes

  • Physical vs Chemical ChangesRequired

    Matter & Materials // Ages 11 to 13

    KS3 physical vs chemical changes extends KS2 reversible vs irreversible changes

Topic // Research-informed

Teaching notes

From the Marble Skill Taxonomy. These notes have not been validated in classrooms, so treat them as a starting point for your own judgement.

The approach

For 9–10 year olds learning that dissolving, mixing, and changes of state are reversible (no new substance is made and the original material can be recovered). The core method is do-and-undo: perform a change, perform the action that reverses it, and confirm the SAME material has returned. Contrast this with an irreversible change (e.g. toasting bread) where a new substance forms. Emphasise conservation — the material persists even when it looks gone — and have learners judge by 'was a new substance made?' rather than by appearance or by whether heat was involved.

Common misconceptions

  • Melting or dissolving destroys or uses up the material.
  • All changes can be undone (over-generalising reversibility to burning/cooking).
  • A change of state makes a new substance rather than the same substance in a new state.
  • Mixing is irreversible because the materials 'became one thing'.
  • If a material looks different after a change, it must be a different material.

Useful representations

  • A do-and-undo bench with forward and reverse controls per station
  • Reverse-arrow pairs (melt⇄freeze, dissolve⇄evaporate, mix⇄filter)
  • A 'same material recovered?' confirmation indicator
  • A greyed-out reverse control on an irreversible teaser (burnt toast)

Teaching practices

  • Pair every reversible change with the action that reverses it (do-and-undo) and confirm the SAME material returns.
  • Group the canonical reversible set — changes of state, dissolving, and mixing separable materials — under the single test 'no new substance made'.
  • Contrast directly with an irreversible change so the boundary is felt, not just stated.
  • Reinforce conservation: the material persists through the change even when it looks gone.
  • Have pupils predict reversibility and name the reversing action before testing.

Activities to try

  1. 1

    The do-it, undo-it bench

    Why it works: A reversible change alters how a material looks or its state but makes NO new substance, so you can get the original material back by undoing it; some changes (toasting) make a new substance and cannot be undone.

    1. At station 1, gently warm a chunk of chocolate (e.g. in a bowl over warm water) only until it flows, then chill it and confirm it sets back into solid chocolate. Overheated chocolate can scorch or burn, which makes new substances and cannot be undone.
    2. At station 2, stir salt into water until it seems to disappear (it is still there, dissolved), then gently heat the dish and confirm salt crystals reappear.
    3. At station 3, tip sand into water, pour the mixture through a filter, and confirm the sand is separated out on the filter (damp, but the same sand) while the water passes through (it may be slightly cloudy if the sand has very fine particles).
    4. For each station, do the change and then the reversing action, and check whether the same material has been recovered before moving on (if using a screen or bench simulation, this may be a forward/reverse control and a 'same material recovered?' indicator).
    5. At a fourth station, an adult toasts a slice of bread; try to think of any action that would turn it back into bread and notice there is none ('you can't un-toast it — a new substance was made'). In a simulation, this may appear as a greyed-out reverse control.
  2. 2

    Reverse-arrow summary chart

    Why it works: The canonical reversible changes — changes of state, dissolving, and mixing separable materials — all share one test: no new substance is formed, so the original can be recovered.

    1. Match each change to its reversing action: melt⇄freeze, dissolve⇄evaporate, mix⇄filter.
    2. Reveal or state what gets you back to the original material for each pair.
    3. Add the single test that unites all three pairs: 'no new substance made'.
  3. 3

    Sort and justify: reversible or not?

    Why it works: Reversibility is judged by whether a new substance was made and the original can be recovered — not by whether heat was added or whether the material looks different.

    1. Categorise a set of changes as reversible or irreversible.
    2. Match each reversible change to the specific action that would reverse it.
    3. For each judgement, state the reason: can the original material be recovered, with no new substance made?
    4. Tackle tricky cases: is dissolving salt reversible even though the water looks completely different? Is re-set chocolate the same substance?

Topic // Standards

Curriculum standards

Codes for the curriculum statements this topic maps to. Each publisher owns its standard text.
The national curriculum in England: Key stages 1 and 2 framework document
Y5.Sci.PCM.5

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