1.4 – Can Matter Change Its State?
🔄 1.4 – Can Matter Change Its State?
🎤 Ask Students:
“Can ice become water?”
“Can water turn into steam?”
“Can we get the ice back from water?”
Let students respond.
Then say:
“Yes! Matter can change from one state to another — and that’s what we’ll explore today.”
🔍 What Is Change of State?
Definition:
Matter can change from solid ↔ liquid ↔ gas when heat is added or removed, or pressure is changed.
These changes are physical changes — the substance remains the same chemically, but its form and energy change.
🔥 Key Processes of State Change
| Change | Process Name |
|---|---|
| Solid → Liquid | Melting |
| Liquid → Solid | Freezing |
| Liquid → Gas | Evaporation / Boiling |
| Gas → Liquid | Condensation |
| Solid → Gas (directly) | Sublimation |
| Gas → Solid (directly) | Deposition |
🧪 Daily Life Examples
-
Ice melts to water
-
Water boils into steam
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Steam condenses on cold surfaces
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Camphor or naphthalene disappears without melting (sublimation)
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Water freezes in ice trays
🌡️ Effect of Heat (Temperature) on State Change
“When we heat a solid, particles gain kinetic energy, move faster, and overcome attraction → it melts.”
“When we cool a liquid, particles slow down and get tightly packed → it freezes.”
🧪 Example: Heating Ice
| Step | Observation | Change |
|---|---|---|
| Ice at 0°C | Starts melting | Solid → Liquid |
| Water at 100°C | Starts boiling | Liquid → Gas |
📘 Note: Temperature stays constant during melting and boiling until the full change is complete. The added heat is used to break bonds, not raise temperature.
🧠 Important Concept: Latent Heat
📘 Latent Heat: The heat energy required to change the state of a substance without changing its temperature.
-
Latent heat of fusion → solid ↔ liquid
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Latent heat of vaporisation → liquid ↔ gas
“This is why water at 100°C stays at 100°C while boiling — all the energy goes into converting it to steam, not heating it further.”
🌬️ Effect of Pressure on State Change
“Did you know we can also change the state of matter by increasing pressure?”
✅ Example:
Gases can be converted into liquids by applying high pressure and low temperature.
That’s how:
-
LPG cylinders store gas in liquid form
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Oxygen cylinders work in hospitals
📌 Class Summary Chart
State Change of Matter
├── Heat ↑ → Solid → Liquid → Gas
├── Heat ↓ → Gas → Liquid → Solid
└── Pressure ↑ + Temp ↓ → Gas → Liquid
💬 Classroom Questions to Ask
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What happens to ice when it is heated?
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What is the boiling point of water?
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Why does the temperature stay constant during melting?
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How do LPG cylinders store gas?
🎤 Closing Line for Class
“Matter may look solid, but with a little heat or pressure — it transforms! Ice becomes water, water becomes vapour — all through the invisible dance of particles.”
Would you like this as a slide deck, worksheet, or want to include Activity 1.8 (heating ice & measuring temperature) next?
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