Question

Explain why surface tension and viscosity decrease with increasing temperature.

Why do substances with high surface tensions also tend to have high viscosities?

Answer 1

1) When the temperature increase the viscosity decreases

because When the temperature increases, the molecules become excited and begin to move more freely.

These movements results in a energy which is enough to overcome the forces that bind the molecules together,

So this allows the liquid to become more fluid

As a result the viscosity decreases.

2)

similarly

when the temperature of a liquid increases, its surface tension decreases.

To put it simply

Surface Tension and viscosity are the result of cohesive forces among the molecules.

As the temperature increases , the number of molecules with sufficient kinetic energy to overcome the forces increases

so the surface tension and visocity decreases with increase in temperature

3)

substances with high surface tensions also tend to have high viscosities?

because

both of them are related to the cohesive forces between the molecules

higher surface tension means higher cohesive forces between the molecules which in turn means higher viscosity