Question

The internal energy of an ideal gas increases during an isothermal process when the gas is
(A) Expanded by adding more molecules to it
(B) Expanded by adding more heat to it
(C) Expanded against zero pressure
(D) Compressed by doing work on it

Answer 1

Hint: Ideal gas does not exist in real life. It is a concept to define the rules the gases are supposed to follow. Ideal gases molecules do not attract or repel each other and the molecules themselves take up no volume. There are no exactly ideal gases.

Complete step by step answer:
We are given that the internal energy of an ideal gas increases during an isothermal process, first of all, let us define the terms coming up. Internal energy is the energy contained inside the gas on account of its molecules. The isothermal process is defined as such a process in which the temperature of the system does not increase or decrease. Internal energy in an isothermal process is directly proportional to the number of molecules plus the temperature of the gas and the Boltzmann constant.
So, the said process can be done by adding more molecules to the existing system, Hence the correct option is (A).

Note: Isothermal processes occur when a system is in contact with a thermal reservoir and the process takes place very slowly. In an isothermal process, the internal energy of an ideal gas is always constant. The external heat always helps in increasing the internal energy of the system.