Year 6 Science · AC9S6U04

AC9S6U04: Compare reversible changes, including dissolving and changes of state, and irreversible changes, including cooking and rusting that produce new substances

Use evidence about substance identity to compare reversible physical changes with irreversible changes that form new substances.

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What students learn in AC9S6U04Start here

Learning intention: Use evidence about substance identity to compare reversible physical changes with irreversible changes that form new substances.

Curriculum focus: Compare reversible changes, including dissolving and changes of state, and irreversible changes, including cooking and rusting that produce new substances.

Success criteria

classify changes using evidence rather than appearance alone
explain dissolving and changes of state as reversible physical changes
recognise cooking and rusting as changes that produce new substances

Key vocabularyOpen section

reversible change: a change that can be undone by a physical process so the original substance is recovered
irreversible change: a change not reversed by simple physical processes, often because new substances form
dissolving: spreading a solute through a solvent to form a solution
change of state: melting, freezing, evaporation or condensation without changing substance identity
new substance: matter with properties and composition different from the starting material
evidence: observations used to support a classification

Investigation and reasoning routineOpen section

Describe the before-and-after observations.
Ask whether the substance identity changed.
Look for combined evidence of a new substance.
Test whether a physical process can recover the original material.
State a classification with evidence or say evidence is insufficient.

classify change

Task: An ice cube melts and the liquid water is frozen again. How should this change be classified?

Model reasoning: A reversible physical change with no new substance formed. Only the state changes; the substance remains water.

use evidence

Task: An ice cube melts and the liquid water is frozen again. Which observation is the strongest evidence for the classification?

Model reasoning: The liquid can freeze back into solid water. This evidence addresses whether the original substance remains or a new substance forms.

recovery or reversal

Task: An ice cube melts and the liquid water is frozen again. Which follow-up action best investigates this change?

Model reasoning: Cool the liquid below its freezing point. This action tests reversibility, recovery, properties or the conditions involved in the change.

particle reasoning

Task: An ice cube melts and the liquid water is frozen again. Which particle-level description is most appropriate at Year 6?

Model reasoning: A change of state changes particle motion and arrangement, not substance identity.

reject misconception

Task: A student says, “All heating creates a new substance.” Which response is best?

Model reasoning: Melting can be reversed by cooling and does not create a new substance.

evaluate evidence

Task: The water looks cloudy after melting, but no further observations are recorded. What is the most scientific conclusion?

Model reasoning: Cloudiness alone is insufficient evidence that a new substance formed. Scientific classification should match the available observations and acknowledge missing evidence.

Curriculum coverage and concept boundaryOpen section

The decisive comparison

Melting, freezing, evaporation, condensation and many dissolving processes keep the same substances and can be reversed physically. Cooking and rusting produce new substances and are not undone by simple cooling or reshaping.

Dissolving is not disappearing

A dissolved solute remains in the solution. Water can often be evaporated to recover crystals, although classroom safety and substance properties determine the method.

Evidence of reaction

A lasting new colour, gas, odour, temperature change or residue may support new-substance formation, especially when several observations agree. One visible change alone is not always decisive.

Separate simultaneous changes

A candle can melt physically and burn chemically. Metal can bend physically and later corrode chemically. Analyse each process rather than applying one label to the whole scene.

Important questions and answersWith answers

Is every heated change irreversible? No. Melting is reversible by cooling; cooking and burning involve new substances.
Does dissolving destroy a solid? No. Solute particles remain dispersed and may be recovered.
Is “hard to undo” enough evidence of a chemical change? No. The key question is whether a new substance formed.

Assessment-style questions and review hintsWith answers

Wet clay is reshaped and later returned to a lump. What is the best classification? Hint: Ask whether a new substance formed.
Copper sulfate solution is safely evaporated by a teacher and crystals remain. What does this show? Hint: Follow both solute and solvent.
A candle wax pool forms while the wick burns. Which analysis is best? Hint: Analyse each observed change separately.
A powder is mixed with water and the beaker feels cooler. What can be concluded? Hint: Avoid certainty from a single sign.
Which comparison best tests whether water is needed for rusting? Hint: Change one proposed cause.
Which pair correctly labels liquid water → gas → liquid water? Hint: Track the starting and ending states.

Support, core and extendOpen section

Support: highlight the changed feature, observation and comparison before writing a claim.
Core: solve an unseen context and justify the answer with precise evidence.
Extend: evaluate a limitation, competing explanation or misleading model while staying within Year 6 science.

Exit ticket and mastery evidenceOpen section

Classify melting ice, dissolving salt and rusting iron. For each, state whether a new substance forms and give one piece of evidence.

Evidence of mastery: The student compares unfamiliar changes using substance identity, recovery methods and cautious evidence, including cases where physical and chemical changes occur together.