Question

According to the Kinetic-Molecular Theory, the kinetic energy of the molecules increases when they are
A.Mixed with other molecules at lower temperature
B.Frozen into a solid
C.Condensed into a liquid
D.Heated to a higher temperature
E.Collide with each other in a container at a lower temperature

Answer 1

Hint: Kinetic energy of the molecules of a gas has direct relation with temperature. This can be understood by two ways: Charles’ law and assumptions of Kinetic Theory of gases. Both of them give the same conclusion that kinetic energy is directly proportional to temperature due to more collisions between molecules at higher temperatures.

Complete step-by-step answer:
The Kinetic Molecular Theory of Gases is derived from the observations made about gases so as to explain their macroscopic properties. The basic assumptions of the Kinetic Molecular Theory are as follows:
The volume occupied by the individual particles of a gas is negligible compared to the volume of the gas itself.
The particles of an ideal gas exert no attractive forces on each other or on their surroundings.
Gas particles are in a constant state of random motion and move in straight lines until they collide with another body.
The collisions exhibited by gas particles are completely elastic; when two molecules collide, total kinetic energy is conserved.
The average kinetic energy of gas molecules is directly proportional to absolute temperature only; this implies that all molecular motion ceases if the temperature is reduced to absolute zero.
We can apply Kinetic Theory to Gas Laws such as Charles’ Law states that at constant pressure, the volume of a gas increases or decreases by the same factor as its temperature and it can be written as:
 \[\dfrac{{{V_1}}}{{{T_1}}} = \dfrac{{{V_2}}}{{{T_2}}}\].
As per the fifth assumption of Kinetic Molecular Theory, an increase in temperature will ultimately increase the average kinetic energy of the molecules. As the particles move faster, they are likely to hit the edge of the container more often and if the reaction occurs at constant pressure, molecules must stay farther apart and an increase in volume will compensate for the increase in particle collision with the surface of the container.
Therefore, we can say that according to the Kinetic-Molecular Theory, the kinetic energy of the molecules increases when they are heated to a high temperature.
Hence the correct option is (D).

Note: Perfect collision means that there is no loss of energy which is actually not possible for any molecule after getting collided with each other with the wall of the system. Gas molecules create pressure due to collision with the walls of the container and these collisions are perfectly elastic. We can also say that no energy is gained or lost in such a case.