Question

Choose the correct statement from the given options.

• A. Higher the surface tension, more is the vapour pressure.
• B. Lower the surface tension, higher is the vapour pressure.
• C. Vapour pressure does not depend upon surface tension.
• D. Variation of vapour pressure with surface tension is given by Clausius – Clapeyron equation.

Answer 1

The correct option is B Lower the surface tension, higher is the vapour pressure.

Vapour pressure depends on:
1. Surface Tension
2. Temperature
Effect of surface tension:
The intermolecular forces at the surface would directly influence the surface tension, which varies inversely with the vapour pressure.

Higher the intermolecular forces, higher is the surface tension and, lower is the vapour pressure.
Effect of temperature on the vapour pressure of a liquid is given by Clausius –Clapeyron equation.

$\ln \left(\frac{P_2}{P_1}\right)=\frac{\Delta H}{R}(\frac{1}{T_1}-\frac{1}{T_2})$

where,

$\Delta H\text{is the enthalpy of vapourisation}{P}_1\text{is the vapour pressure of the liquid at temperature}{T}_1{P}_2\text{is the vapour pressure of the liquid at temperature}{T}_2$

Hence option (b) is correct.