1. The problem statement, all variables and given/known data Which of the following statements about a Carnot engine is true? a) Any Carnot engine has an efficiency of 100% b) Irreversible energies have the greatest possible efficiency. c) Heat can spontaneously flow from a cold reservoir to a hotter reservoir. d) If a process is reversible, the efficiency of an engine is maximum. e) All energies are reversible. 2. Relevant equations None 3. The attempt at a solution Well, I think the answer is E. I canceled out choice b because no where in my text book did it mention irreversible energies having high efficiency. I don't think it's choice a because the third law of thermodynamics says reaching a temperature of absolute zero is impossible and makes it impossible for a Carnot cycle engine to achieve 100% efficiency. So if I'm right, why is E right? If I'm wrong, then why would it be one of the other choices? I pretty much just used process of elimination.