Understanding Surface Tension

Surface tension is a property of liquids that causes them to behave like a stretched elastic membrane. It arises from the cohesive forces between the liquid molecules. Molecules in the bulk of the liquid are surrounded by other molecules and experience balanced forces in all directions. However, molecules at the surface are only attracted to other molecules below and to the sides, resulting in a net inward force. This inward force pulls the surface molecules closer together, minimizing the surface area.

Effect of Temperature on Surface Tension

Temperature is a measure of the average kinetic energy of the molecules in a substance. When the temperature of a liquid increases, the molecules gain kinetic energy and move faster. This increased movement and energy weaken the intermolecular cohesive forces. The cohesive forces are responsible for surface tension. As the temperature rises, the cohesive forces weaken, and the inward pull on the surface molecules decreases. Consequently, the surface tension of the liquid decreases as the temperature increases. Conversely, when the temperature of a liquid decreases, the molecules lose kinetic energy and move slower. The cohesive forces between the molecules become stronger relative to their kinetic energy. This leads to a stronger inward pull on the surface molecules, increasing the surface tension.

Surface Tension of Water and Temperature Relationship

For water, just like most liquids, the surface tension is strongly dependent on temperature. The cohesive forces (hydrogen bonds) between water molecules are affected by temperature. * As the temperature of water increases, the hydrogen bonds weaken and break more easily. This reduction in cohesive forces leads to a decrease in surface tension. * As the temperature of water decreases, the hydrogen bonds are stronger and more numerous. This increase in cohesive forces leads to an increase in surface tension. This relationship is inverse: surface tension increases when temperature decreases, and decreases when temperature increases.

Analyzing the Options

Let's look at the given options based on our understanding:

• Increase with decrease in temperature: This aligns with the principle that lower temperature strengthens cohesive forces, increasing surface tension.
• Decreases with decrease in temperature: This is the opposite of the expected behavior.
• Independent of temperature: Surface tension is significantly affected by temperature, so this is incorrect.
• None of these: This would be true only if the other options were incorrect.

Based on the relationship between temperature and surface tension, the surface tension of water increases as its temperature decreases.