Question

ASSERTION: The final temperature of an ideal gas in adiabatic expansion is less in reversible expansion than in irreversible expansion against a constant external pressure.
REASON: The magnitude of work done by an ideal gas in the adiabatic expansion is more in a reversible process than that in an irreversible process.
A.Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
B.Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
C.Assertion is correct but Reason is incorrect
D.Assertion is incorrect but Reason is correct

Answer 1

Hint: During adiabatic expansion, the gas is allowed to expand quickly work is done by the gas during its expansion. So, its internal energy decreases. As heat can't be entering the same system for the surroundings, the temperature of gas falls.

Complete answer:
An adiabatic expansion has less work done and no heat flow, thereby a lower internal energy compared to an isothermal expansion which has both heat flow and work done. Temperature decreases during adiabatic expansion. In science, a process that is not reversible is called irreversible. This concept arises frequently in thermodynamics.
During a reversible adiabatic expansion process, because of no heat transfer and no internal molecular/frictional dissipation, only work transfer takes place from high pressure to low pressure. Hence all the useful energy is fully utilized for work transfer with NO internal/external loss (irreversibility).
However, during the irreversible expansion process, there will be a change (increase) of entropy of the system because of frictional dissipation. This dissipated energy will be transferred (lost) from the system as thermal energy. Hence, whatever useful energy is available at the beginning of expansion, a fraction of that is dissipated because of irreversibility. Therefore, final temperature at the end of the irreversible process is lesser corresponding to the reversible adiabatic one (under same pressure limits) where, no degradation of energy takes place
Thus, we know that Both assertion and reason are correct and reason is the correct explanation for Assertion.

Therefore, the correct answer is option (A).

Note: It is an idealized thermodynamic process that is adiabatic and in which the work transfers of the system are frictionless; there is no transfer of heat or of matter and the process is reversible.