Question

A heat engine executes one complete cycle. The change in entropy of the engine (just the engine, not the external thermal reservoirs) is:

• A. zero
• B. greater than zero
• C. less than zero
• D. depends on the type of engine

Answer 1

The correct option is A zero

In one complete cycle, the engine returns to its original state. So all macroscopic variables (N, V, T, S etc) must return to their original state and the change is zero. Remember, even though heat is a path variable, the entropy S is a state variable, hence this stamen will be true even for an irreversible process.