Exam 21: Heat Engines and Refrigerators

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?

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

One of the most efficient engines built so far has the following characteristics: combustion chamber temperature = 1900°C exhaust temperature = 430°C 7.0 × 10⁹ cal of fuel produces 1.4 × 10¹⁰ J of work in one hour,where 1 cal = 4.19 J (a)What is the actual efficiency of this engine? (b)What is the Carnot efficiency of the engine? (c)What is the power output of this engine?

A 2.00 kg piece of lead at 40.0°C is placed in a very large quantity of water at 10.0°C,and thermal equilibrium is eventually reached.Calculate the entropy change of the lead that occurs during this process.The specific heat of lead is 130 J/(kg ∙ K).

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

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?

The graph in the figure shows a cycle for a heat engine for which =35 J.What is the thermal efficiency of this engine?

A 810-g quantity of ethanol,in the liquid state at its melting point of is frozen at atmospheric pressure.The heat of fusion of ethanol is 1.04 × 10⁵ J/kg,the molecular mass is 46.1 g/mol,and the ideal gas constant is R = 8.314 J/(mol ∙ K).The change in the entropy of the ethanol as it freezes is closest to

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

A 610-g quantity of an ideal gas undergoes a reversible isothermal compression at a temperature of The compression reduces the volume of the gas from initially,to finally.The molecular mass of the gas is and the ideal gas constant is R = 8.314 J/(mol ∙ K).The entropy change for the gas is closest to

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.

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

You want to design an ideal Carnot heat engine that wastes only 35.0% of the heat that goes into it.The lowest cold-reservoir temperature available to you is +15.0°C.If 150.0 J of work is done per cycle,the heat input per cycle is closest to

A Carnot engine is operated as a heat pump to heat a room in the winter.The heat pump delivers heat to the room at the rate of per second and maintains the room at a temperature of when the outside temperature is The power requirement for the heat pump under these operating conditions is closest to

The temperature inside a Carnot refrigerator placed in a kitchen at 22.0°C is 2.0°C.The heat extracted from the refrigerator is 89 MJ/h.What power is needed to operate this refrigerator?

A perfect Carnot engine operates between the temperatures of 300K and 700K,drawing 60 kJ of heat from the 700K reservoir in each cycle.How much heat is dumped into the 300K reservoir in each cycle?

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

A certain engine extracts 1300 J of heat from a hot temperature reservoir and discharges 700 J of heat to a cold temperature reservoir.What is the efficiency of this engine?

A Carnot refrigerator takes heat from water at 0°C and rejects heat to a room at 12°C.Suppose that 92.0 grams of water at 0°C are converted to ice at 0°C by the refrigerator.Calculate the mechanical energy that must be supplied to the refrigerator.The heat of fusion of water is 3.34 × 10⁵ J/kg.

What is the change in entropy of 10.0 moles of ideal monatomic gas that reversibly undergoes the isothermal expansion shown in the figure? The ideal gas constant is R = 8.314 J/(mol ∙ K).