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Question: Answered & Verified by Expert
Choose the correct statement with respect to the vapour pressure of a liquid among the following :
ChemistrySolutionsJEE Main
Options:
  • A Increases non-linearly with increasing temperature
  • B Decreases non-linearly with increasing temperature
  • C Decreases linearly with increasing temperature
  • D Increases linearly with increasing temperature
Solution:
2291 Upvotes Verified Answer
The correct answer is: Increases non-linearly with increasing temperature

The pressure exerted by the vapors over the liquid surface when liquid and vapour are in equilibrium is called vapour pressure. Vapour pressure increases with an increase with temperature.
Average kinetic energy of the gas molecules is directly proportional to the absolute temperature. At higher temperatures, more molecules from the liquid have enough KE to escape from the surface of the liquid. Which will increase vapor pressure.

For phase equilibrium for liquid & vapour phases

dP dT = Δ S Δ V = Δ H vap T . Δ V vap

dP dT = Δ H vap T RT P = Δ H vap × P RT 2 for 1 mole

dP P = Δ H vap RT 2 dT

The relation between temperature and vapor pressure is given by the Clausius-Clapeyron equation.

ln P 2 P 1 = Δ H vap R T 2 - T 1 T 1 T 2

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ie. vapour increases exponentially with rise in temp ie.
Non linear increase.

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