Question

With increase in temperature, the viscosity of ______.

1. gases decreases.
2. liquids increases.
3. gases increases.
4. liquids decreases.

Answer 1

c and d

Explanation:

The viscosity of gases increases with the increase in temperature, because of the increasing temperature the rate of diffusion increases.

The viscosity of liquid decreases with the increase in temperature, because the cohesive force between the liquid molecules decreases with the increase in temperature.

Relation between the coefficient of viscosity and temperature (Andrade formula)

`η = (Ae^(Cρ/T))/(ρ^(-1/3))`

Where T = Absolute temperature of the liquid, p = density of a liquid and A and C are constants.

Important point: With the increase in temperature, the coefficient of viscosity of liquids decreases but that of gases increases. The reason is that as temperature rises, the atoms of the liquid become more mobile, whereas in the case of a gas, the collision frequency of atoms increases as their motion becomes more random.