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Exam 20: Second Law of Thermodynamics

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Question 21

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Give the Clausius statement of the Second Law of Thermodynamics.

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Heat can flow spontaneously fr...

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Question 22

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A Carnot cycle engine operates between a low temperature reservoir at 20°C and a high temperature reservoir at 800°C. If the engine is required to output 20.0 kJ of work per cycle, how much heat must the high temperature reservoir transfer to the engine during each cycle?

A) 27.5 kJ
B) 73.2 kJ
C) 39.2 kJ
D) 800 kJ
E) 20.5 kJ

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Question 23

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An air conditioner with a coefficient of performance of 3.5 uses 30 kW of power. How much power is it discharging to the outdoors?

Give the Kelvin-Planck statement of the Second Law of Thermodynamics.

A heat engine operating at maximum efficiency has an efficiency of 35.0%. The temperature of the hot reservoir is 700 K. What is the temperature of the cold reservoir?

Natural processes tend to move toward a state of less disorder.

FIGURE 20-2 -A monatomic ideal gas reversibly follows the process shown in Fig. 20-2 starting from state A at a temperature 300 K and ending at state B. (a) What is the final temperature of the gas? (b) What is the change in internal energy of the gas in going from state A to state B? (c) What is the change in entropy of the gas in going from state A to state B?

A Carnot cycle consists of

A heat pump has a coefficient of performance that is 60% of the Carnot heat pump coefficient of performance. The heat pump is used to heat a home to 24.0°C during the winter with the low temperature reservoir at the outdoor temperature. At which outdoor temperature would it be more efficient to add the energy directly to the interior of the home than use it to run the heat pump?

Which has the larger entropy: a gas that occupies only half of a container, with the other half a vacuum, or the same gas occupying the entire container?

Explain the following statement: "In any natural process, some energy becomes unavailable to do useful work."

Heat will flow spontaneously from a cold object to a hot object.

Describe the Carnot cycle.

A heat engine with an efficiency of 30.0% performs 2500 J of work. How much heat is discharged to the lower temperature reservoir?

What is the coefficient of performance of a Carnot heat pump used to remove heat from ice at 0.0°C and add heat to a room at 20.0°C?

A refrigerator has a coefficient of performance equal to 4.2. How much work must be done on the refrigerator in order to remove 250 J of heat from the interior?

On a hot day, you open the refrigerator and experience a refreshing feeling when the cool air comes in contact with your body. You think to yourself "I think that I'll just keep the refrigerator door open and stand in front of the refrigerator all day today to stay cool. I might even bring a chair." Will this work? Explain why or why not.

All reversible engines operating between the same two temperatures have the same efficiency.

Sketch the schematic diagram of energy transfers for a heat engine.

In any natural process, some energy becomes unavailable to do useful work.