Question

With an increase in temperature the viscosity of:
A). Gases decreases and liquid increases
B). Gases increases and liquid decrease
C). Both gases and liquid increases
D). Both gases and liquid decreases

Answer 1

Hint: Viscosity is the measure of degree momentum transport in a fluid perpendicular to the flow of velocity due to flow sheer. The intermolecular forces in liquid and gases are different, when the temperature is raised they show the change in viscosity.

Complete step-by-step solution:
Viscosity is a measure of degree momentum transport in a fluid perpendicular to the flow of velocity due to flow shear. According to the kinetic theory of gases, viscosity is proportional to the square root of absolute temperature.
In liquid, there will be molecular interchange similar to those in gases.
There are additional substantial attractive, cohesive forces between the molecules of a liquid. Here both cohesion and molecular interchange contribute to liquid viscosity.
The impact of increasing the temperature of a liquid is to reduce these cohesive forces and increase the rate of the molecular interchange. This effect causes a decrease in shear stress while the latter causes it to increase. Therefore, liquid shows a decrease in viscosity with increasing temperature.
Gases are made up of particles that are very far apart. When the temperature has increased the particles of gas move faster and collide more often, resulting in greater resistance of friction. The more is the friction in gases the more is its viscosity.
Therefore, option B) is correct, that is with increasing temperature the viscosity of gases increases, and liquid decreases.

Additional information:
When we consider liquid at room temperature, the molecules are tightly bound together by attractive intermolecular force (Van der Waal forces).
Van der Waals forces include attraction and repulsions between atoms, molecules, and surfaces as well as other intermolecular forces.

Note: The physical and chemical properties of solids, liquids and gases are all different. The intermolecular forces are different in all of them. In solids, the bonds on atoms are very strong, and intermolecular forces are strong. In liquid, the atoms are loosely bound and have weak intermolecular forces and in gases, the atoms are not bound; they move freely and thereby very weak intermolecular forces.