Solutions for Chapter 20: The Second Law of Thermodynamics

20.1DQ) A pot is half-filled with water, and a lid is placed on it, forming a tight seal so that no water vapor can escape. T...

20.1E) A diesel engine performs 2200 J of mechanical work and discards 4300 J of heat each cycle. (a) How much heat must be ...

20.2DQ) Give two examples of reversible processes and two examples of irreversible processes in purely mechanical systems, su...

20.2E) An aircraft engine takes in 9000 J of heat and discards 6400 J each cycle. (a) What is the mechanical work output of ...

20.3DQ) What irreversible processes occur in a gasoline engine? Why are they irreversible?

20.3E) A Gasoline Engine. A gasoline engine takes in 1.61 X 104 J of heat and delivers 3700 J of work per cycle. The heat is...

20.4DQ) Suppose you try to cool the kitchen of your house by leaving the refrigerator door open. What happens? Why? Would the...

20.4E) A gasoline engine has a power output of 180 kW (about 241 hp). Its thermal efficiency is 28.0%. (a) How much heat mus...

20.5DQ) A member of the U.S. Congress proposed a scheme to produce energy as follows. Water molecules (H2O) are to be broken ...

20.5E) The pV-diagram in ?Fig. E20.5 shows a cycle of a heat engine that uses 0.250 mol of an ideal gas with ? = 1.40. Proce...

20.6DQ) Is it a violation of the second law of thermodynamics to convert mechanical energy completely into heat? To convert h...

20.6E) (a) Calculate the theoretical efficiency for an Otto-cycle engine with ? = 1.40 and r = 9.50. (b) If this engine take...

20.7DQ) Imagine a special air filter placed in a window of a house. The tiny holes in the filter allow only air molecules mov...

20.7E) The Otto-cycle engine in a Mercedes-Benz SLK230 has a compression ratio of 8.8. (a) What is the ideal efficiency of t...

20.8DQ) An electric motor has its shaft coupled to that of an electric generator. The motor drives the generator, and some cu...

20.8E) The coefficient of performance K = H/P is a dimensionless quantity. Its value is independent of the units used for H ...

20.9DQ) When a wet cloth is hung up in a hot wind in the desert, it is cooled by evaporation to a temperature that may be 20 ...

20.9E) A refrigerator has a coefficient of performance of 2.10. In each cycle it absorbs 3.40 ×104 J of heat from the cold r...

20.10DQ) Compare the ?pV?-diagram for the Otto cycle in Fig. 20.6 with the diagram for the Carnot heat engine in Fig. 20.13. E...

20.10E) A room air conditioner has a coefficient of performance of 2.9 on a hot day and uses 850 W of electrical power. (a) H...

20.11DQ) If no real engine can be as efficient as a Carnot engine operating between the same two temperatures, what is the poi...

20.11E) A refrigerator has a coefficient of performance of 2.25, runs on an input of 95 W of electrical power, and keeps its ...

20.12DQ) The efficiency of heat engines is high when the temperature difference between the hot and cold reservoirs is large. ...

20.12E) A freezer has a coefficient of performance of 2.40. The freezer is to convert 1.80 kg of water at 25.0o C to 1.80 kg ...

20.13DQ) What would be the efficiency of a Carnot engine operating with TH = TC? What would be the efficiency if TC = 0 K and ...

20.13E) A Carnot engine whose high-temperature reservoir is at 620 K takes in 550 J of heat at this temperature in each cycle...

20.14DQ) Real heat engines, like the gasoline engine in a car, always have some friction between their moving parts, although ...

20.14E) A Carnot engine is operated between two heat reservoirs at temperatures of 520 K and 300 K. (a) If the engine receive...

20.15DQ) Does a refrigerator full of food consume more power if the room temperature is 20o C than if it is 15o C? Or is the p...

20.15E) A Carnot engine has an efficiency of 59% and performs 2.5 × 104 J of work in each cycle. (a) How much heat does the e...

20.16DQ) In Example 20.4, a Carnot refrigerator requires a work input of only 230 J to extract 346 J of heat from the cold res...

20.16E) An ice-making machine operates in a Carnot cycle. It takes heat from water at 0.0o C and rejects heat to a room at 24...

20.17DQ) Explain why each of the following processes is an example of increasing randomness: mixing hot and cold water; free e...

20.17E) A Carnot refrigerator is operated between two heat reservoirs at temperatures of 320 K and 270 K. (a) If in each cycl...

20.18DQ) The free expansion of an ideal gas is an adiabatic process and so no heat is transferred. No work is done, so the int...

20.18E) A certain brand of freezer is advertised to use 730 kW ? h of energy per year. (a) Assuming the freezer operates for ...

20.19DQ) Are the earth and sun in thermal equilibrium? Are there entropy changes associated with the transmission of energy fr...

20.19E) A Carnot heat engine has a thermal efficiency of 0.600, and the temperature of its hot reservoir is 800 K. If 3000 J ...

20.20DQ) Discuss the entropy changes involved in the preparation and consumption of a hot fudge sundae.

20.20E) A Carnot heat engine uses a hot reservoir consisting of a large amount of boiling water and a cold reservoir consisti...

20.21DQ) If you run a movie film backward, it is as if the direction of time were reversed. In the time-reversed movie, would ...

20.21E) You design an engine that takes in 1.50 × 104 J of heat at 650 K in each cycle and rejects heat at a temperature of 3...

20.22DQ) BIO Some critics of biological evolution claim that it violates the second law of thermodynamics, since evolution inv...

20.22E) A 4.50-kg block of ice al 0.00°C falls into the ocean and melts. The average temperature of the ocean is 3.50°C, incl...

20.23DQ) BIO A growing plant creates a highly complex and organized structure out of simple materials such as air, water, and ...

20.23E) A sophomore with nothing better to do adds heat to 0.350 kg of ice at 0.0o C until it is all melted. (a) What is the ...

20.24E) ?You decide to take a nice hot bath but discover that your thoughtless roommate has used up most of the hot water. Yo...

20.25E) A 15.0-kg block of ice at 0.0o C melts to liquid water at 0.0o C inside a large room at 20.0o C. Treat the ice and th...

20.26E) CALC You make tea with 0.250 kg of 85.0o C water and let it cool to room temperature (20.0o C). (a) Calculate the ent...

20.27E) Three moles of an ideal gas undergo a reversible isothermal compression at 20.0o C. During this compression, 1850 J o...

20.28E) What is the change in entropy of 0.130 kg of helium gas at the normal boiling point of helium when it all condenses i...

20.29E) (a) Calculate the change in entropy when 1.00 kg of water

20.30E) ?(a) Calculate the change in entropy when 1.00 mol of water (molecular mass 18.0 g / mol ) at \(100^{\circ} \mathrm{C...

20.31E) A 10.0-L gas tank containing 3.20 moles of ideal He gas at 20.0°C is placed inside, completely evacuated, insulated b...

20.32E) A box is separated by a partition into two parts of equal volume. The left side of the box contains 500 molecules of ...

20.33E) ?CALC Two moles of an ideal gas occupy a volume V. The gas expands isothermally and reversibly to a volume 3V. (a) Is...

20.34E) CALC A lonely party balloon with a volume of 2.40 L and containing 0.100 mol of air is left behind to drift in the te...

20.35P) CP An ideal Carnot engine operates between 500o C and 100o C with a heat input of 250 J per cycle. (a) How much heat ...

20.36P) You are designing a Carnot engine that has 2 mol of CO2 as its working substance; the gas may be treated as ideal. Th...

20.37P) A certain heat engine operating on a Carnot cycle absorbs 150 J of heat per cycle at its hot reservoir al 135°C and h...

20.38P) BIO Entropy of Metabolism. An average sleeping person metabolizes at a rate of about 80 W by digesting food or burnin...

20.39P) BIO Entropy Change from Digesting Fat. Digesting fat produces 9.3 food calories per gram of fat, and typically 80% of...

20.40P) A heat engine takes 0.350 mol of a diatomic ideal gas around the cycle shown in the p?V-diagram of ?Fig. P20.36. Proc...

20.41P) CALC You build a heat engine that takes 1.00 mol of an ideal diatomic gas through the cycle shown in ?Fig. P20.39?. (...

20.42P) Heat Pump?. A heat pump is a heat engine run in reverse. In winter it pumps heat from the cold air outside into the w...

20.43P) CALC A heat engine operates using the cycle shown in ?Fig. P20.41?. The working substance is 2.00 mol of helium gas, ...

20.44P) CP As a budding mechanical engineer, you are called upon to design a Carnot engine that has 2.00 mol of a monatomic i...

20.45P) An experimental power plant at the Natural Energy Laboratory of Hawaii generates electricity from the temperature gra...

20.46P) What is the thermal efficiency of an engine that operates by taking n moles of diatomic ideal gas through the cycle s...

20.47P) CALC A cylinder contains oxygen at a pressure of 2.00 atm. The volume is 4.00 L, and the temperature is 300 K. Assume...

20.48P) BIO Human Entropy. A person with skin of surface area 1.85 m2 and temperature 30.0°C is resting in an insulated room ...

20.49P) CP BIO A Human Engine. You decide to use your body as a Carnot heat engine. The operating gas is in a tube with one e...

20.50P) ?Entropy Change Due to the Sun. Our sun radiates from a surface at 5800 K (with an emissivity of 1) into the near-vac...

20.51P) A monatomic ideal gas is taken around the cycle shown in ?Fig. P20.46 in the direction shown in the figure. The path ...

20.52P) A Stirling-Cycle Engine?. The ?Stirling cycle is similar to the Otto cycle, except that the compression and expansion...

20.53P) A Carnot engine operates between two heat reservoirs at temperatures TH and TC. An inventor proposes to increase the ...

20.54P) A typical coal-fired power plant generates 1000 MW of usable power at an overall thermal efficiency of 40%. (a) What ...

20.55P) Automotive Thermodynamics. A Volkswagen Passat has a six-cylinder Otto-cycle engine with compression ratio r = 10.6. ...

20.56P) An air conditioner operates on 800 W of power and has a performance coefficient of 2.80 with a room temperature of 21...

20.57P) Unavailable Energy. ?The discussion of entropy

20.58P) ?The maximum power that can be extracted by a wind turbine from an air stream is approximately\(P=k d^2 v^3\)where d ...

20.59P) ?CALC (a) For the Otto cycle shown in Fig. 20.6, calculate the changes in entropy of the gas in each of the constant-...

20.60P) A ?TS?-Diagram?. (a) Graph a Carnot cycle, plotting Kelvin temperature vertically and entropy horizontally. This is c...

20.62P) To heat 1 cup of water to make coffee,

20.63P) ?CALC An object of mass \(m_{1}\) specific heat \(c_{1}\) and temperature \(T_{1}\) is placed in contact with a secon...

20.64CP) Consider a Diesel cycle that starts (at point a in Fig. 20.7) with air at temperature Ta. The air may be treated as a...