When the temperature of a liquid is increased, its surface tension?

Analysis

This question tests your understanding of the molecular behavior of liquids and the concept of surface tension in relation to thermal energy.

Concept Explanation

Surface tension is the result of cohesive forces between molecules at the surface of a liquid. These molecules are pulled inward by the molecules beneath them, creating a "skin" or tension.

When you increase the temperature of a liquid:

1. Increased Kinetic Energy: The molecules gain more kinetic energy and move faster.
2. Weakened Cohesive Forces: As the molecules move more vigorously, the intermolecular forces (cohesive forces) that hold them together become weaker.
3. Reduced Tension: Since surface tension is directly dependent on the strength of these cohesive forces, as the forces weaken, the surface tension of the liquid decreases.

Step-by-Step Solution

1. Identify the relationship: Surface tension is a measure of the strength of the attractive forces between liquid molecules.
2. Apply heat: Adding heat increases the thermal agitation of the molecules.
3. Observe the effect: This agitation disrupts the orderly arrangement and the strength of the intermolecular bonds at the surface.
4. Conclusion: Because the bonds are weakened by the increased temperature, the surface tension must decrease.

Exam Tip

Think of surface tension like a "tightly knit group of friends holding hands." If you make them run around and get very excited (increase temperature), they won't be able to hold onto each other as tightly. Therefore, the "tension" in their grip decreases!