Sublimation and Effect of Pressure

Sublimation

Some substances change directly from solid to gas without becoming liquid!

🧪 Activity 1.13: Camphor Sublimation

Procedure:

1. Crush some camphor
2. Put in china dish
3. Cover with inverted funnel (cotton plug on stem)
4. Heat slowly

Observation: Camphor vapour deposits as solid on funnel walls!

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Key Definitions

Sublimation

Change of state directly from solid → gas without passing through liquid state.

Examples:

• Camphor
• Naphthalene balls (disappear over time!)
• Dry ice (solid CO₂)

Deposition

Change of state directly from gas → solid without passing through liquid state.

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Effect of Pressure 📊

What happens when we apply pressure to a gas?

• Particles come closer together
• Volume decreases
• Can eventually liquefy!

Applying pressure + Reducing temperature can liquefy gases.

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Dry Ice 🧊

What is it?

• Solid carbon dioxide (CO₂)
• Stored under high pressure

Special property: When pressure decreases to 1 atmosphere, solid CO₂ converts directly to gas (sublimation)!

That's why it's called "dry ice" — it doesn't become wet (liquid)!

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State Diagram 🔄

             SUBLIMATION
    SOLID ←---------------→ GAS
      ↑                      ↑
      | MELTING    BOILING   |
      | (Fusion)   (Vaporisation)
      ↓                      ↓
    SOLID ←----→ LIQUID ←----→ GAS
          FREEZING    CONDENSATION

All State Changes:

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Key Takeaway 💡

Pressure and temperature together determine the state of a substance!