Exam 21: Degradation of Energy

A Carnot engine operates between reservoirs at 550K and 300K,discarding 1500 J of heat in each cycle. (a)What is the engine's efficiency? (b)How much heat is supplied to the engine by the hot reservoir in each cycle?

The compressor in a certain Carnot refrigerator performs 480 J of work to remove 150 J of heat from the interior of the refrigerator.How much heat must the coils behind the refrigerator discharge into the kitchen?

A real (non-Carnot)heat engine,operating between heat reservoirs at temperatures of 650 K and 270 K,performs 4.3 kJ of net work and rejects 8.0 kJ of heat in a single cycle.The thermal efficiency of this heat engine is closest to

According to the second law of thermodynamics,the entropy of any system always increases.

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

An ideal reversible refrigerator keeps its inside compartment at 9.0°C.What is the high temperature,T_h,needed to give this refrigerator a coefficient of performance of 3.7?

A 2.00-kg block of ice at 0.00°C is dropped into a very large lake at 25.0°C and completely melts.For water,the heat of fusion is 3.35 × 10⁵ J/kg,the heat of vaporization is 2.25 × 10⁵ J/kg,and the specific heat is 4190 J/kg•K.The net change in entropy of the system consisting of the ice and the lake due to this melting process is closest to

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?

A refrigerator removes heat from the freezing compartment at the rate of 20 kJ and ejects 24 kJ into a room per cycle. How much work is required in each cycle?

A Carnot engine operating between a reservoir of liquid mercury at its melting point (233 K)and a colder reservoir extracts 10.0 J of heat from the mercury and does 8.0 J of work during each cycle.What is the temperature of the colder reservoir?

Is it possible to transfer heat from a hot reservoir to a cold reservoir?

What is the maximum theoretical efficiency possible for a heat engine operating between a reservoir in which ice and water coexist,and a reservoir in which water and steam coexist? The pressure is constant at 1.0 atmosphere for both reservoirs.

Is it possible to transfer heat from a cold reservoir to a hot reservoir?

A Carnot refrigerator has a coefficient of performance of 2.5.The refrigerator consumes 50 W of power.How much heat is removed from the interior of the refrigerator in 1 hour?

An ideal Carnot engine operates between reservoirs having temperatures of 125°C and -20°C.Each cycle the heat expelled by this engine is used to melt 30.0 g of ice at 0.00°C.The heat of fusion of water is 3.34 × 10⁵ J/kg and the heat of vaporization of water is 2.25 × 10⁶ J/kg. (a)How much work does this engine do each cycle? (b)How much heat per cycle does this engine absorb at the hot reservoir?

A certain Carnot heat pump transfers energy from the outside of a house,where the temperature is -15°C,to the inside of a room where the temperature is 21°C.If this heat pump runs off of electricity,what is the minimum rate at which it uses electrical energy to deliver 150 W to the inside room?

An automobile engine takes in 4000 J of heat and performs 1100 J of mechanical work in each cycle. (a) Calculate the engine's efficiency. (b) How much heat is "wasted" in each cycle?

An engine manufacturer makes the claim that the engine they have developed will,on each cycle,take 100 J of heat out of boiling water at 100°C,do mechanical work of 80 J,and exhaust 20 J of heat at 10°C.What,if anything,is wrong with this claim?

The entropy of an isolated system must be conserved,so it never changes.

A refrigerator has a coefficient of performance of 1.15,and it extracts 7.95 J of heat from the cold reservoir during each cycle. (a)How much work is done on the gas in each cycle? (b)How much heat is exhausted into the hot reservoir in each cycle?