work must be done on the gas to return it to its original volume

1. An adiabatic free expansion of a gas in a thermally isolated container is not reversible because _____ . Select the correct answer. • work must be done on the gas to return it to its original volume • heat must be exchanged with the surroundings to return the gas to its original temperature • its internal energy has a greater value after the expanded gas is returned to its original volume and temperature • of all of these things • work must be done on a gas to return it to its original volume, and heat must be exchanged with the surroundings to return the gas to its original temperature

2. In an engine operating in the Otto cycle, the final volume of the fuel-air mixture is one ninth the initial volume. Assume γ = 1.4 . The maximum theoretical efficiency of this cycle is _____ %. (0°C = 273.15K) Select the correct answer. • 58 • 53 • 47 • 76 • 82

3. A lawn mower has a 3-horsepower engine (1 HP = 750 W). If the engine has an efficiency of 20%, and the throttle is such that the engine cycles 15 times a second, the heat that is expelled in one cycle is _____ . Select the correct answer. • 600 J • 750 J • 30 J • 550 J • 700 J

4. A gasoline engine absorbs 3,000 J of heat at 300°C and expels 1000 J at a temperature of 50°C. The change in entropy (in J/K) for the system is _____ . (0°C = 273.15K) select the correct answer. • 2.1 • 10.0 • 1.7 • 3.0 • 3.4

5. An ideal heat engine can have an efficiency of 1 if the temperature of the low temperature reservoir is _____ . Select the correct answer. • 0K • 0°C • 0°F • 0°R • the same as the temperature of the heat source

6. A gasoline engine absorbs 2,700 J of heat and performs 1,100 J of mechanical work in each cycle. The amount of heat expelled in each cycle is _____ . Select the correct answer. • 1.600 J • 1.100 J • 2.700 J • 1.700 J • 1.800 J

7. An automobile engine operates with an overall efficiency of 28%. How much energy is delivered as waste heat (in gallons of gasoline) for each 10 gallons of fuel burned? Select the correct answer. • 7.2 • 2.8 • 7.9 • 5.8 • 5.0

8. The change in entropy when 1 kg of ice melts at 0°C is (in J/K) _____ . (Lice = 333J/g) (0°C = 273.15K) Select the correct answer. • 1,219 • 1,341 • 1,463 • 853 • 731

9. A refrigerator has a coefficient of performance of 5. If the refrigerator absorbs 29 cal of heat from the cold reservoir in each cycle, the heat expelled (in cal) into the heat reservoir is _____ . Select the correct answer. • 34.8 • 24.2 • 36.3 • 43.5 • 19.3

10. An engine is designed to obtain energy from the temperature gradient of the ocean. What is the thermodynamic efficiency of such an engine if the temperature of the surface of the water is 57°F (14°C) and the temperature well below the surface is 39°F (4°C) ? (0°C = 273.15K) Select the correct answer. • 3.5% • 71% • 32% • 7.5% • 10%