Question

Pressure of an ideal gas is increased by keeping temperature constant. What is the effect on kinetic energy of molecules?
(A) Increase
(B) Decrease
(C) No change
(D) Cannot be determined

Answer 1

Hint: In order to know the effect on kinetic energy of the molecule, we must know about the kinetic molecular theory. On knowing this we can explain what happens to the kinetic energy when the temperature is kept constant.

Complete Solution :
Before going to the question given, let us first understand about the Kinetic molecular theory. This theory is the simple macroscopic model that explains about different gas laws. This theory is based on the following five postulates which is given below:
- Gases are composed or made up of the molecules which are in a continuous motion. These gaseous molecules will be travelling in a straight line and will change the directions only when they collide with walls of the container or the nearby molecule.
- The molecules that will compose to give the gas are negligibly small compared to the distance between them.
- The pressure which is exerted by a gaseous molecule will result from the collision of the gaseous molecule with the wall of the container.
- The collision of the gaseous molecule is elastic.
- The average kinetic energy of the gas is directly proportional to the temperature of the gas (in Kelvin).
i.e. \[K.E = \dfrac{3}{2}{K_B}T\]
- Now let us come to the question given. In this question, it is given that the temperature will remain constant when the pressure is increased. As we know from the above postulates that kinetic energy is directly proportional to the temperature. Therefore, when the temperature is constant there will be no change in the kinetic energy of the molecules.
So, the correct answer is “Option C”.

Note: There are different gas laws which are present, they are
- Boyle's law
- Charles law
- Avogadro law
- Gay-Lussac Law.