Question

The internal energy of a monatomic ideal gas is:
A) only kinetic
B) only potential
C) partly kinetic and partly potential
D) none

Answer 1

Hint: The internal energy of a monatomic ideal gas arises from the movement of the gas molecules due to their thermal energy. For a monatomic ideal gas, we assume that the gas molecules do not interact with each other.

Complete step by step answer
The internal energy of the system is a thermodynamic property of the system which is the sum of the kinetic and potential energy of particles that form the system. However, for an ideal gas, we assume that the particles in an ideal gas do not interact.
Since there is no interaction between the particles, there is no potential energy associated with the particles, the internal energy of the system will only be due to the kinetic energy of the system.
The kinetic energy of the system will be proportional to the temperature of the gas. This kinetic energy is associated with the random translational motion of the gas molecules inside the system. The internal energy of the system is also a state function which means that for an ideal gas, the internal energy only depends on the initial and final temperature of the system and not on how the temperature of the system changes.

So the correct choice is option (A).

Note
For a real gas, the internal energy of the system is stored both in the form of kinetic and potential energy as the gas molecules interact with each other and hence they have potential energy associated with each other. The internal energy cannot be measured directly and is usually measured based on the temperature of the system.