💧 What is Vapour Pressure?

 Sure! Here's a simple and clear explanation of vapour pressure, specially tailored for Class 12 Chemistry students:

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💧 What is Vapour Pressure?

Vapour pressure is the pressure created by the vapour (gas) of a liquid when it is in equilibrium with the same liquid in a closed container at a given temperature.

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🔁 Imagine This:

You pour water into a container and seal it tightly.

• Some water molecules escape into the air above the liquid — this is evaporation.

• After a while, some of these vapour molecules start returning to the liquid — this is condensation.

Eventually, the rate of evaporation = rate of condensation.
At this point, the vapour molecules exert a certain pressure — this is called the:

✅ Vapour Pressure

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📈 Factors Affecting Vapour Pressure:

1. Temperature
   🔺 Higher temperature → more molecules escape → higher vapour pressure
   🔻 Lower temperature → fewer molecules escape → lower vapour pressure

2. Nature of Liquid (Volatility)

   • Volatile liquids like acetone, alcohol: high vapour pressure

   • Less volatile liquids like water, glycerin: lower vapour pressure

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🧪 Real-Life Examples:

• The smell of perfume or nail polish remover is due to high vapour pressure — they evaporate easily.

• Water takes time to dry because its vapour pressure is relatively lower.

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📝 Class 12 Board Definition:

Vapour pressure of a liquid is the pressure exerted by its vapour when the liquid and vapour are in dynamic equilibrium at a given temperature.

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Let me know if you want a graphical explanation, a numerical example, or a video script on this topic!