Answer: Is <= 0.
- A Is usually positive
- B Is usually negative
- C Is >= 0 for reversible, < 0 for irreversible
- D Is <= 0
Correct answer: D. Is <= 0
Explanation: Clausius inequality: contour integral of dQ/T <= 0. Equality holds for reversible processes; strict inequality for irreversible.
The Carnot cycle alternates two isothermal steps (heat absorbed at TH, released at TC) with two adiabatic steps (no heat exchange); the enclosed loop area equals the net work output, and η = 1−TC/TH is the maximum possible efficiency between those two temperatures.
Concept context
Laws of thermodynamics, heat engines, entropy, and gas processes.