Question

In a thermodynamic system, working substance is ideal gas, its internal energy is in the form of
(A) Kinetic Energy
(B) Kinetic and Potential Energy
(C) Potential Energy
(D) None of the above

Answer 1

Hint: it is given in the question that the working substance in a thermodynamic system is ideal gas. Now , when asked on internal energy, the internal energy is produced due to the intermolecular forces that happen between gas molecules. Deduce the logic using this.

Complete answer:
A gas is considered to be an ideal gas in a particular case where the collisions between atoms and molecules are absolutely elastic in nature and doesn’t have intermolecular forces of attraction. The atoms and molecules of ideal gas won’t attract or repel each other. Ideal gas doesn’t get expanded by themselves and takes up volume. The ideal gas law is charted based upon the behavior of gases to ideal gases. These are often considered as simple gases.
Now, it is given that the ideal gas is used as a working substance in a thermodynamic system. Internal energy of the system is often associated with the atoms or molecules present in the gas. We know that ,in ideal gas, there are no intermolecular forces. If a force is applied on the gas , the gas particles according to the kinetic theory of gases will have infinite distance which means that the potential energy will be zero.
Thus, the internal energy of the system depends upon the kinetic energy of the gas molecules.

Hence, option (a) is the right answer for the given question.

Note: In kinetic theory of gases, one of the postulates states that the average kinetic energy of the gas particles directly depends upon the temperature of the system. Now, in a thermodynamic system, there will be heat transfer from system to surrounding or surrounding to system, which really implies change in temperature.