Question

Why does the viscosity of a liquid decrease with temperature, and why does the viscosity of a gas increase with temperature?

a) Increased temperature increases cohesive forces in liquids.
b) Increased temperature reduces cohesive forces in liquids.
c) Increased temperature decreases collisions in gases.
d) Increased temperature increases collisions in gases.

Answer 1

The viscosity of liquids decreases with temperature due to reduced cohesive forces, while the viscosity of gases increases due to more frequent molecular collisions.

Step-by-step explanation:

Effect of Temperature on Viscosity of Liquids and Gases

The viscosity of a liquid decreases with temperature because increased temperature leads to increased kinetic energy among the molecules. This increased motion allows molecules to more easily overcome cohesive forces that bind them together, making the liquid flow more readily. In contrast, the viscosity of a gas increases with temperature primarily because increased temperature leads to a higher average kinetic energy, which in turn causes molecules to move more rapidly. This results in more frequent and energetic collisions between the molecules, thus increasing the resistance to flow, or viscosity.

Motor oils are a practical application of these principles. They must be able to function effectively across a wide temperature range, and understanding the relationship between temperature and viscosity is essential for designing oils that can maintain optimal performance in different conditions.