When a liquid and its vapour are at equilibrium and the pressure is suddenly decreased:
Show Hint
- Vapour pressure of solution increases
- Heating occurs
- Cooling occurs
- Equilibrium remains unaffected
The Correct Option is C
Solution and Explanation
When the system is at liquid-vapour equilibrium and external pressure is suddenly decreased, the system is disturbed.
Step 2: Analysis
According to Le Chatelier's principle, the system will try to restore equilibrium by increasing its vapour pressure to match the new lower external pressure. To do this, more liquid molecules must escape into the vapour phase, which requires energy (enthalpy of vaporization).
Step 3: Conclusion
Since the energy for vaporization is taken from the surroundings (the liquid itself), the liquid cools down. This is the principle behind refrigeration and why boiling under reduced pressure lowers the boiling point.
Final Answer: (C)
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