Question

Ashar has water at different temperatures.

(1) ${25}^{\circ }C$ (2) ${50}^{\circ }C$ (3) ${75}^{\circ }C$ (4) ${90}^{\circ }C$

He is wondering where vapour pressure of water will be highest.

Can you help him and choose the correct order of vapour pressure for him.

• A. 4 > 3 > 2 > 1
• B. 3 > 2 > 4 > 1
• C. 1 > 2 > 3 > 4
• D. 2 > 3 > 4 > 1

Answer 1

The correct option is A 4 > 3 > 2 > 1

It is a straight forward question. We just need to relate vapour pressure and temperature.

For that, let's recall definition of vapour pressure.

The vapour pressure of a liquid at any temperature is defined as the pressure exerted by the vapour in equilibrium with the liquid at that temperature.

$\Rightarrow$ More molecules in vapour phase lead to more vapour pressure.

$\Rightarrow$ At higher temperature, more number of molecules escape into vapour phase.

Therefore, as temperature increases, the vapour pressure increases because at higher temperatures, large number of molecules escape into the vapour phase.