A heat engine receives 1,000 kJ of heat from a source at 527 °C and rejects heat to surroundings at 27 °C. What is the maximum possible efficiency, the maximum work output, and the minimum heat rejected?
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Worked answer. Use absolute temperatures: T_H = 527 + 273 = 800 K, T_C = 27 + 273 = 300 K.
- Carnot (maximum) efficiency η = 1 − T_C/T_H = 1 − 300/800 = 0.625 = 62.5 %.
- Maximum work W = η × Q_H = 0.625 × 1,000 = 625 kJ.
- Minimum heat rejected Q_C = Q_H − W = 375 kJ.
No real engine reaches this; friction and finite-rate heat transfer make processes irreversible. Using °C instead of kelvin is the classic error.
Original UniCircle question. Last reviewed 21 Oct 2026.