Title: Entropy and Exergy Summary Questions

Entropy True/False Question

Q: Entropy is always conserved during a process.
A: false

Q: In a completely reversible process, the generated entropy is always positive.
A: false

Q: Changes in entropy during a process are caused by the following mechanisms:
- Heat Transfer
- Mass Transfer
- Irreversibilities
- All Answers Listed (correct)

Q: Consider a heat transfer process in which heat is added to the system. This causes:
- An increase in the system's entropy (correct)
- A decrease in the system's entropy
- No effect on the system entropy

Q: A high-quality energy can:
- produce more work output than a low quality energy (correct)
- produce less work output than a low quality energy
- produce the same or less work output than a low quality energy

Q: Exergy is a measure of:
- The maximum work potential of an energy given a set of conditions. (correct)
- The actual work output an energy given a set of conditions.
- The average work potential of an energy given a set of conditions.

Q: How is second-law efficiency different from the first-law (thermal) efficiency?
- It compares the actual work done to the maximum theoretical work possible. (correct)
- It compares the actual work to the input energy.
- It compares the input to the maximum theoretical work possible.

HE - 2nd Law Efficiency

Q: A heat engine feeds heat to a sink at 300K. It has a thermal efficiency of 25% and a second-law efficiency of 50%. What temperature is the heat source at?
- 600K (correct)
- 300K
- 500K
- 700K