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This lesson covers the changes of state between solids, liquids and gases, as required by the Edexcel GCSE Chemistry specification (1CH0, Topic 1). You need to understand each type of change of state, how energy is involved, and how to interpret heating and cooling curves. A key point is that changes of state are physical changes — they are reversible, and no new substances are formed.
There are six changes of state you need to know:
| Change of State | From | To | Energy Change |
|---|---|---|---|
| Melting | Solid | Liquid | Energy absorbed (endothermic) |
| Freezing | Liquid | Solid | Energy released (exothermic) |
| Boiling / Evaporating | Liquid | Gas | Energy absorbed (endothermic) |
| Condensing | Gas | Liquid | Energy released (exothermic) |
| Sublimation | Solid | Gas (directly) | Energy absorbed (endothermic) |
| Deposition | Gas | Solid (directly) | Energy released (exothermic) |
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