Question

When the temperature is raised, the viscosity of liquid decreases this is because of
A. The decrease in volume of the solution.
B. The increased attraction between the molecules.
C. The decrease in covalent and hydrogen bond forces.
D. The increase in temperature increases the average kinetic energy of the molecules, which overcomes the attractive forces between them.

Answer 1

Hint: Viscosity is defined as the resistance of a fluid (liquid or gas) to change its shape or movement concerning its neighbouring molecules. It is represented by the symbol ‘$\eta $’. To put it in a simple way viscosity is the resistance against the flow of liquid.

Complete Step by Step Solution:
The viscosity of the liquid decreases with a temperature rise. As temperature increases, there is an increase in molecular interchange as the molecule’s speed increases with the rising temperature. That is as temperature rises, molecules possess high kinetic energy and thus overcome the intermolecular force of attraction and move faster.

Whereas in the case of gases, a rise in temperature increases the viscosity of gases as the rise in kinetic energy increases the collision between the molecules and decreases the ability of molecules as a whole to engage in a coordinated move.
Hence the correct option is D.

Note: The viscosity can also be discussed for solids and liquids. Solids don’t have the ability to change their shape and so have a very high viscosity and are often referred to as having infinite viscosity. Here the key point is the rise in kinetic energy helps the molecules to overcome the Intermolecular forces, which further helps in the flow of liquid.