Chapter 12, Problem 12.60P

Interpretation Introduction

Interpretation:

The reason for the lower surface tension of aqueous solution of ethanol $\left({\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}\text{OH}\right)$ than water is to be determined.

Concept introduction:

The molecules on the surface and bulk experience different intermolecular forces. The molecule in bulk is surrounded by the molecules from all sides. Therefore the net force on the molecules is zero. On the other hand, molecules on the surface have molecules only below them so the net attractive force experienced by them is in downward direction.

Due to the net attractive forces, the surface molecules will try to move into the bulk and surface area decreases.

Surface tension is the energy that is needed to raise the surface area by a given amount. The unit of surface tension is ${\text{J/m}}^2$. Surface tension is directly related to the intermolecular forces and therefore increases with increase in the intermolecular forces.