Question

Why is entropy change during reversible adiabatic expansion always zero?

Answer 1

Entropy: Entropy is a measure of a system's disorder or randomness.

Adiabatic: A process is said to be adiabatic if no heat enters or exits the system at any point during the process, according to thermodynamics.

1. The system covers the path and returns to its original state through reversible processes, resulting in a net change in heat of zero.
2. The changes in the reversible process do not impact the entropy of the system or the entropy of the environment, resulting in a zero change in entropy.
3. Entropy change $∆S=\frac{d{q}_{rev}}{T}$, where for reversible adiabatic expansion $d{q}_{rev}=0$, and $T$ is the temperature.
4. As a result, for an adiabatic process, the change in entropy equals zero.

Thus, Entropy change during reversible adiabatic expansion is always zero.