In an isolated system, which process yields zero entropy change?

In an isolated system, which process yields zero entropy change?

• A. Irreversible process
• B. Reversible process
• C. Any process
• D. None

Answer: (B)

In an isolated system, entropy can only change due to internal production, since there is no exchange of energy or matter with the surroundings. A reversible process proceeds without dissipative effects, so no extra entropy is created and the system’s entropy stays the same. If the process is irreversible—owing to factors like friction or rapid mixing—internal irreversibilities generate additional entropy, causing the entropy to increase. Therefore, zero entropy change corresponds to a reversible process in an isolated system.

In an isolated system, entropy can only change due to internal production, since there is no exchange of energy or matter with the surroundings. A reversible process proceeds without dissipative effects, so no extra entropy is created and the system’s entropy stays the same. If the process is irreversible—owing to factors like friction or rapid mixing—internal irreversibilities generate additional entropy, causing the entropy to increase. Therefore, zero entropy change corresponds to a reversible process in an isolated system.