When a substance gains or loses energy, its particles can overcome or re-form the forces of attraction between them, causing a change of state. Changes of state are physical changes — no new substances are formed, and the process is reversible.
| Change of State | Direction | Energy Change |
|---|---|---|
| Melting | Solid → Liquid | Energy absorbed |
| Freezing | Liquid → Solid | Energy released |
| Evaporating / Boiling | Liquid → Gas | Energy absorbed |
| Condensing | Gas → Liquid | Energy released |
| Subliming | Solid → Gas | Energy absorbed |
| Depositing | Gas → Solid | Energy released |
State symbols in equations show the physical state of each substance:
- (s) = solid
- (l) = liquid
- (g) = gas
- (aq) = aqueous (dissolved in water)
Quick Check: Iodine crystals can turn directly from a solid to a purple gas when gently warmed. What is this process called?
Sublimation. Iodine sublimates — it goes directly from solid to gas without passing through a liquid stage. The reverse (gas directly to solid) is called deposition.
This deep dive covers Changes of State within States of Matter for GCSE Chemistry. Revise States of Matter in Atomic Structure for GCSE Chemistry with 12 exam-style questions and 10 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 4 of 13 in this topic. Use this deep dive to connect the idea to the wider topic before moving on to questions and flashcards.
Practice questions for States of Matter
Which of the following best describes the arrangement of particles in a solid?
A heating curve shows a flat section (plateau) when a solid is being heated to become a liquid. Explain why the temperature does not rise during this flat section. [3 marks]