56. Kinetic theory of an ideal gas is based upon the following assumption(s)

(A) Gases are made of molecules with negligible volume

(B) The gaseous molecules do not possess kinetic energy

(C) The molecules are in constant random motion

(D) Intermolecular forces of attraction are negligible

Kinetic Theory of an Ideal Gas – Assumptions, Concepts, and Complete Explanation

Correct Answer

(A), (C), and (D)

Introduction to the Kinetic Theory of Gases

The kinetic theory explains the macroscopic properties of gases, such as pressure, temperature, and volume, by considering the microscopic motion of gas molecules. According to this theory, an ideal gas consists of a very large number of tiny molecules that move continuously in all possible directions and collide with each other as well as with the walls of the container.

The pressure exerted by a gas is the result of continuous collisions of gas molecules with the walls of the container. The temperature of the gas is directly related to the average kinetic energy of its molecules.

Explanation of Each Option

Option (A): Gases are made of molecules with negligible volume

This statement is correct. One of the basic assumptions of the kinetic theory is that the individual gas molecules occupy an extremely small volume compared to the total volume of the container. For an ideal gas, the molecular volume is considered negligible, allowing the gas to occupy the entire available space uniformly.

This simplification makes the mathematical treatment of gases much easier and is one of the defining assumptions of an ideal gas.

Option (B): The gaseous molecules do not possess kinetic energy

This statement is incorrect. In fact, the entire kinetic theory is based on the idea that gas molecules are continuously moving and therefore possess kinetic energy. The average kinetic energy of gas molecules depends only on the absolute temperature of the gas.

If gas molecules had no kinetic energy, they would remain stationary, collisions would not occur, and gases would not exert pressure. Therefore, this assumption directly contradicts the kinetic theory.

Option (C): The molecules are in constant random motion

This statement is correct. Gas molecules are assumed to move continuously in random directions. Their motion is completely irregular, and they frequently collide with one another and with the container walls.

These random collisions are perfectly elastic in an ideal gas, meaning there is no loss of kinetic energy during collisions. Continuous random motion is one of the most important assumptions of the kinetic theory.

Option (D): Intermolecular forces of attraction are negligible

This statement is correct. In an ideal gas, the attractive and repulsive forces between molecules are assumed to be negligible except during collisions. Because of the absence of significant intermolecular forces, gas molecules move freely throughout the container.

This assumption is reasonably accurate for gases at low pressure and high temperature, where the molecules remain far apart from one another.

Summary of the Assumptions of the Kinetic Theory of an Ideal Gas

The kinetic theory is based on several important assumptions. Gas molecules have negligible volume compared to the container, they remain in continuous random motion, collisions between molecules and container walls are perfectly elastic, intermolecular forces are negligible except during collisions, and the average kinetic energy of the molecules depends only on the absolute temperature.

These assumptions successfully explain many observable properties of gases, including Boyle’s law, Charles’s law, Gay-Lussac’s law, and the ideal gas equation.

Why Option (B) is Incorrect

The statement that gaseous molecules do not possess kinetic energy is fundamentally opposite to the kinetic theory. The theory derives the pressure and temperature of gases from the kinetic energy of moving molecules. Therefore, without kinetic energy, the theory itself would have no physical basis.

Final Answer

Correct Options: (A), (C), and (D)

The assumptions of the kinetic theory of an ideal gas include negligible molecular volume, continuous random motion of molecules, and negligible intermolecular forces. The statement that gas molecules do not possess kinetic energy is incorrect because molecular kinetic energy is the fundamental basis of the kinetic theory.