Sublimation
Sublimation and Thermal Effects: Sublimation
Sublimation
Sublimation
What you'll learn
- Most solids melt into a liquid before turning into gas. But some solids can turn directly into gas, without ever becoming liquid. This is called sublimation.
- Common examples: camphor (kapur), naphthalene balls (mothballs), dry ice (solid carbon dioxide), iodine crystals, and some solid air-freshener blocks.
- The reverse process — a gas changing directly into a solid — is called deposition. Frost forming on a very cold window from water vapour in the air is an everyday example of deposition.
Key concepts
Level 1 — What is sublimation?
Verbal: Sublimation is the change of state where a solid turns directly into a gas, skipping the liquid state completely.
Symbolic: Solid → Gas (directly, no liquid stage).
| Substance | What you observe | Change of state |
|---|---|---|
| Camphor (kapur) | Slowly disappears, no liquid left behind | Sublimation |
| Naphthalene balls | Shrink away in a wardrobe over weeks | Sublimation |
| Dry ice | Turns into cold fog/gas, no wet puddle | Sublimation |
| Iodine crystals (heated) | Give off violet vapour directly | Sublimation |
Level 2 — Sublimation vs melting/evaporation
Verbal: Melting and evaporation both pass through a liquid stage (solid → liquid → gas). Sublimation skips the liquid stage entirely (solid → gas directly).
Real-life: Ice melts into water first, then the water evaporates — that is NOT sublimation. But camphor never becomes a liquid puddle — that IS sublimation.
Worked example
A camphor tablet placed in an open dish becomes smaller and smaller over a few days, with no liquid puddle ever forming. What change of state is happening?
Step 1 — Camphor starts as a solid.
Step 2 — It never becomes a liquid; no puddle appears.
Step 3 — It slowly turns into gas (vapour) that spreads into the air.
Answer: This is sublimation — solid directly to gas.
Common mistakes
| Mistake | Why it happens | Fix |
|---|---|---|
| Thinking camphor "evaporates" like water | Confusing with liquid evaporation | Camphor never becomes liquid, so it sublimes, not evaporates |
| Thinking sublimation only happens to ice | Overgeneralising | Ice normally melts first; camphor, naphthalene, and dry ice are true subliming solids |
| Forgetting the reverse process has its own name | Not linking related terms | Gas to solid directly is called deposition |
Quick check
- Name two substances that sublime.
- What is the reverse of sublimation called?
- How is sublimation different from evaporation?
Stretch: Why is dry ice useful for transporting ice cream compared to ordinary ice?
Revision tip: Remember: sublimation always skips the liquid stage — solid straight to gas.
Open the Practice tab for graded questions on Sublimation.
Key Takeaways (TL;DR)
- What you'll learn
- Key concepts
- Worked example
- Common mistakes
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