Question

Which factor affects the surface tension of a liquid?

• A. Specific volume
• B. Viscosity
• C. Density
• D. Temperature

Hint:

With an increase in temperature:
- Intermolecular cohesive forces decrease.
- Consequently, the surface tension of the liquid always decreases.
At the critical temperature, surface tension becomes exactly zero.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Surface tension is a physical property of liquids arising from cohesive forces between molecules at the fluid interface.
Any factor that alters these intermolecular attractive forces will directly influence the surface tension of the liquid.

Step 2: Detailed Explanation:
Temperature has a highly significant and direct effect on the surface tension of a liquid.
As the temperature of a liquid increases, the kinetic energy of its molecules increases, leading to more vigorous molecular motion.
This increased thermal agitation weakens the intermolecular cohesive forces holding the liquid molecules together.
Since surface tension is a direct manifestation of these cohesive forces, any reduction in cohesion leads to a corresponding decrease in surface tension.
Mathematically, this relationship is often represented by Eötvös' rule or other empirical equations, showing that surface tension decreases almost linearly with temperature.
At the critical temperature of the liquid, the intermolecular forces become negligible, and the surface tension drops to zero.
In contrast, parameters like specific volume, viscosity, and density are physical properties but do not directly govern or alter the surface tension forces in the same causative manner as temperature does.

Step 3: Final Answer:
Temperature is the primary factor that affects the surface tension of a liquid.