Can Matter Change Its State?

🔄 1.4 – Can Matter Change Its State?

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🎤 Start with a Simple Question

“Can ice turn into water? Can water become steam?
And what’s really happening to the particles when this change happens?”

✨ Let students respond. Then say:

“Yes, matter can change its state, and inside, the particles are moving, separating, and absorbing energy during these changes.”

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🧊 Change from Solid to Liquid (Melting / Fusion)

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🔬 Activity: Melting Ice (Lab-Based)

Steps:

1. Take a beaker with crushed ice and a thermometer.

2. Heat it slowly.

3. Note:

   • The temperature when ice starts melting.

   • The temperature when all the ice turns into water.

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📘 What Happens During Melting?

• On heating, particles gain kinetic energy.

• They start vibrating faster, overcoming inter-particle attraction.

• At a point (melting point), particles break free from fixed positions.

• Ice → Water

📌 Melting Point of Ice: 273.15 K or 0°C

💡 The process is called Fusion.

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❓ Why Temperature Stays Constant at 0°C While Ice Melts?

Because the heat energy doesn’t increase temperature — it is used to break bonds between solid particles.
This energy is called:

📘 Latent Heat of Fusion

"The amount of heat required to change 1 kg of a solid into liquid at its melting point without changing its temperature."

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💧 Change from Liquid to Gas (Boiling / Vaporisation)

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🔬 Activity: Boiling Water

Steps:

1. Continue heating the water formed after melting.

2. Use a glass rod to stir.

3. Note the temperature when water starts boiling.

4. Observe till most of it converts to steam.

📌 Boiling Point of Water: 373 K or 100°C

Boiling is a bulk phenomenon — not just the surface, but all particles in the liquid gain enough energy to turn into vapour.

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💡 Latent Heat of Vaporisation

📘 Definition:

"The heat required to convert 1 kg of liquid into gas at its boiling point without a temperature rise."

✅ Water at 100°C and steam at 100°C are different — steam has more energy due to latent heat.

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🔁 Changing State by Temperature and Pressure

Matter changes state not just by heating/cooling, but also by changing pressure.

✅ Example:

• Gas → Liquid: LPG or oxygen is compressed into cylinders by increasing pressure and cooling.

• Dry ice (solid CO₂) sublimates due to low pressure.

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🌫️ Sublimation – Solid to Gas Directly

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🔬 Activity 1.13: Sublimation of Camphor

Steps:

1. Take crushed camphor in a china dish.

2. Cover with an inverted funnel and cotton plug in the stem.

3. Heat gently.

4. Observe: Solid camphor disappears → Vapours condense on funnel walls.

✅ Inference: Camphor sublimes — it goes directly from solid to gas.

📘 Definition:

“The change of state from solid to gas without becoming liquid is called sublimation.”
The reverse (gas to solid) is called deposition.

✅ Other subliming substances: Naphthalene, iodine, ammonium chloride

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🧠 Key Takeaways for Students

Process	Change	Heat Used
Melting (Fusion)	Solid → Liquid	Breaks attraction
Boiling/Vaporising	Liquid → Gas	Breaks attraction completely
Sublimation	Solid → Gas	Direct change
Condensation	Gas → Liquid	Heat released
Freezing	Liquid → Solid	Heat released

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💬 Ask Students:

1. What is latent heat?

2. Why doesn’t temperature rise while ice melts?

3. Can you name substances that sublimate?

4. How does pressure help in changing state?

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🎤 Closing Line for Class:

“Matter is always moving. With a little heat or pressure, a solid can melt, a liquid can boil, and sometimes — like camphor — matter can even skip a step and become gas. Science is full of surprises!”

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