Exam 20: The Second Law of Thermodynamics

A Carnot air conditioner operates between an indoor temperature of 20°C and an outdoor temperature of 39°C.How much energy does it need to remove 2000 J of heat from the interior of the house?

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.

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?

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?

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 of work is done per cycle,the heat input per cycle is closest to

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?

A brass rod,75.0 cm long and having a cross-sectional area of 2.50 cm²,conducts heat from a large furnace at 375°C into a very large cold water bath at 10.0°C without losing any heat at the lateral surface of the rod.Steady state has been established,and the thermal conductivity of brass is .The rate at which the entropy of the system (furnace plus water)is changing is closest to

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 2.0-kg block of aluminum at 50°C is dropped into 5.0 kg of water at 20°C and the temperature is allowed to stabilize.What is the total change in entropy during this process,assuming no heat is exchanged with the environment? The specific heat of aluminum is 910 J/(kg • K)and the specific heat of water is 4190 J/(kg • K).

A coal-fired plant generates 600 MW of electric power.The plant uses of coal each day.The heat produced by the combustion of coal is .The steam that drives the turbines is at a temperature of 300°C,and the exhaust water is at 37°C. (a)What is the overall efficiency of the plant for generating electric power? (b)What is the maximum efficiency that this plant could possibly have using the same temperature extremes that it presently uses? (c)How much thermal energy is exhausted each day by this plant?

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

At atmospheric pressure,45 moles of liquid helium are vaporized at its boiling point of The heat of vaporization of helium,at atmospheric pressure,is and the atomic weight of helium is The change in the entropy of the helium,as it vaporizes,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?

An ice cube at 0°C is placed in a very large bathtub filled with water at 30°C and allowed to melt,causing no appreciable change in the temperature of the bath water.Which one of the following statements is true?

A heat engine takes 2.0 moles of an ideal gas through the reversible cycle abca,on the pV diagram shown in the figure.The path bc is an isothermal process.The temperature at c is 820 K,and the volumes at a and c are 0.010 m³ and 0.16 m³,respectively.The molar heat capacity at constant volume,of the gas,is ,and the ideal gas constant is .The thermal efficiency of the engine is closest to

A hot piece of iron is thrown into the ocean and its temperature eventually stabilizes.Which of the following statements concerning this process is correct? (There may be more than one correct choice.)

During each cycle of operation,a refrigerator absorbs 230 J of heat from the freezer and expels 356 J of heat to the room.How much work input is required in each cycle?

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 of work per cycle,how much heat must the high temperature reservoir transfer to the engine during each cycle?

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 .The entropy change for the gas is closest to

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