An adiabatic free expansion of a gas in a thermally isolated container is not reversible because
A) work must be done on the gas to return it to its original volume.
B) heat must be exchanged with the surroundings to return the gas to its original temperature.
C) its internal energy has a greater value after the expanded gas is returned to its original volume and temperature.
D) of all of the above.
E) of (a) and (b) above only.

Question

Quizplus · Accepted Answer

In an adiabatic free expansion, the gas does not exchange heat with its surroundings because the system is thermally isolated. However, to return the gas to its original volume, work must be done on it, which cannot be fully recovered due to the nature of the expansion being free (no external pressure applied against which the gas does work). This makes the process irreversible. Heat exchange (choice B) and a change in internal energy after returning to the original state (choice C) are not reasons for the irreversibility in this context.

An Adiabatic Free Expansion of a Gas in a Thermally