According to the second law, what can be said about the entropy change in an isolated system?

According to the second law, what can be said about the entropy change in an isolated system?

• A. ΔS < 0
• B. ΔS > 0 only
• C. ΔS ≥ 0
• D. ΔS = 0 always

Answer: (C)

The second law tells us that in an isolated system the entropy cannot decrease. Entropy measures how many microscopic ways the system’s components can be arranged for the same macroscopic state. In a spontaneous process inside an isolated system, the system tends to explore more possible microstates, so the entropy increases or, in the ideal case of a perfectly reversible process, stays the same. Real processes are usually irreversible, producing a positive entropy change. So the entropy change must satisfy ΔS ≥ 0, being zero only for ideal reversible processes and positive for irreversible ones.

The second law tells us that in an isolated system the entropy cannot decrease. Entropy measures how many microscopic ways the system’s components can be arranged for the same macroscopic state. In a spontaneous process inside an isolated system, the system tends to explore more possible microstates, so the entropy increases or, in the ideal case of a perfectly reversible process, stays the same. Real processes are usually irreversible, producing a positive entropy change. So the entropy change must satisfy ΔS ≥ 0, being zero only for ideal reversible processes and positive for irreversible ones.