lesson
Can the original material be recovered?
1 · Learn
Melting ice and freezing the water again are reversible state changes. Dissolved salt can be recovered by allowing the water to evaporate.
Reversible does not mean a change reverses itself instantly or that every mixed material is easy to recover perfectly. State the method and what original material it recovers.
2 · Worked example
I explain how cooling can return liquid water to ice. The substance remains water through that state-change cycle.
3 · Your turn
Is tearing paper the same kind of change as melting ice? Would freezing glue the torn pieces back together?
Check your answer
No. Tearing changes the pieces physically but is not a solid-liquid state change. Freezing does not restore the original intact sheet.
4 · Apply your learning
Sort safe described changes by whether and how original materials can be recovered. Explain uncertain cases rather than forcing every example into a simple label.
Adult guidance and safety
Use pictures or safe adult-approved materials; no heating or chemical mixing by children.
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Check a calculation · Year 5 onward
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