Question

Entropy of universe, in the case of adiabatic expansion of a gas is ________________.

• A. $\Delta$$S_{univ}=O$
• B. $\Delta$$S_{univ}>O$
• C. $\Delta$$S_{univ}
• D. $\Delta$$S_{univ}$$\ge$$O$

Answer 1

The correct option is A $\Delta$$S_{univ}=O$

The entropy change of a system during for a reversible, adiabatic process is zero

Entropy is NOT constant in all adiabatic processes.

The change in entropy for a process is defined as

As Entropy is a state function this equation is valid between any two states.

However it is worth mentioning that the path taken should be a reversible path while calculating the entropy between these states.

So, in a reversible adiabatic process as Qrev = 0, the change in entropy is zero.

Where as for a irreversible process it wouldn’t be zero due to entropy generation.