Chapter 10 Powerpoint

Chapter Presentation Transparencies Sample Problems Visual Concepts Standardized Test Prep Resources Chapter 10 - Thermodynamics

Table of Contents Section 1 Relationships Between Heat and Work Section 2 The First Law of Thermodynamics Section 3 The Second Law of Thermodynamics Thermodynamics Chapter 10

Objectives Recognize that a system can absorb or release energy as heat in order for work to be done on or by the system and that work done on or by a system can result in the transfer of energy as heat. Compute the amount of work done during a thermodynamic process. Distinguish between isovolumetric, isothermal, and adiabatic thermodynamic processes. Section 1 Relationships Between Heat and Work Chapter 10

Heat, Work, and Internal Energy Heat and work are energy transferred to or from a system. An object never has “heat” or “work” in it; it has only internal energy. Chapter 10 Section 1 Relationships Between Heat and Work

Heat, Work, and Internal Energy, continued In thermodynamic systems, work is defined in terms of pressure and volume change. Chapter 10 Section 1 Relationships Between Heat and Work

Heat, Work, and Internal Energy, continued If the gas expands, as shown in the figure,  V is positive, and the work done by the gas on the piston is positive. If the gas is compressed,  V is negative, and the work done by the gas on the piston is negative. (In other words, the piston does work on the gas.) Chapter 10 Section 1 Relationships Between Heat and Work

Heat, Work, and Internal Energy, continued When the gas volume remains constant, there is no displacement and no work is done on or by the system. Although the pressure can change during a process, work is done only if the volume changes. Chapter 10 Section 1 Relationships Between Heat and Work

Thermodynamic Processes An isovolumetric process is a thermodynamic process that takes place at constant volume so that no work is done on or by the system. An isothermal process is a thermodynamic process that takes place at constant temperature. An adiabatic process is a thermodynamic process during which no energy is transferred to or from the system as heat. Chapter 10 Section 1 Relationships Between Heat and Work

Thermodynamic Processes Chapter 10 Section 1 Relationships Between Heat and Work

Objectives I llustrate how the first law of thermodynamics is a statement of energy conservation. Calculate heat, work, and the change in internal energy by applying the first law of thermodynamics. Apply the first law of thermodynamics to describe cyclic processes. Section 2 The First Law of Thermodynamics Chapter 10

Energy Conservation If friction is taken into account, mechanical energy is not conserved. Consider the example of a roller coaster: A steady decrease in the car’s total mechanical energy occurs because of work being done against the friction between the car’s axles and its bearings and between the car’s wheels and the coaster track. If the internal energy for the roller coaster (the system) and the energy dissipated to the surrounding air (the environment) are taken into account, then the total energy will be constant. Chapter 10 Section 2 The First Law of Thermodynamics

Energy Conservation Chapter 10 Section 2 The First Law of Thermodynamics

Energy Conservation, continued The principle of energy conservation that takes into account a system’s internal energy as well as work and heat is called the first law of thermodynamics. The first law of thermodynamics can be expressed mathematically as follows:  U = Q – W Change in system’s internal energy = energy transferred to or from system as heat – energy transferred to or from system as work Chapter 10 Section 2 The First Law of Thermodynamics

Signs of Q and W for a system Chapter 10 Section 2 The First Law of Thermodynamics

Sample Problem The First Law of Thermodynamics A total of 135 J of work is done on a gaseous refrigerant as it undergoes compression. If the internal energy of the gas increases by 114 J during the process, what is the total amount of energy transferred as heat? Has energy been added to or removed from the refrigerant as heat? Chapter 10 Section 2 The First Law of Thermodynamics

Sample Problem, continued 1. Define Given: W = –135 J  U = 114 J Chapter 10 Section 2 The First Law of Thermodynamics Tip: Work is done on the gas, so work (W) has a negative value. The internal energy increases during the process, so the change in internal energy (  U) has a positive value. Diagram: Unknown: Q = ?

Sample Problem, continued 2. Plan Choose an equation or situation: Apply the first law of thermodynamics using the values for  U and W in order to find the value for Q .   U = Q – W Chapter 10 Section 2 The First Law of Thermodynamics Rearrange the equation to isolate the unknown: Q =  U + W

Sample Problem, continued 3. Calculate Substitute the values into the equation and solve: Q = 114 J + (–135 J) Q = –21 J Chapter 10 Section 2 The First Law of Thermodynamics Tip: The sign for the value of Q is negative. This indicates that energy is transferred as heat from the refrigerant.

Sample Problem, continued 4. Evaluate Although the internal energy of the refrigerant increases under compression, more energy is added as work than can be accounted for by the increase in the internal energy. This energy is removed from the gas as heat, as indicated by the minus sign preceding the value for Q. Chapter 10 Section 2 The First Law of Thermodynamics

First Law of Thermodynamics for Special Processes Chapter 10 Section 2 The First Law of Thermodynamics

Cyclic Processes A cyclic process is a thermodynamic process in which a system returns to the same conditions under which it started. Examples include heat engines and refrigerators. In a cyclic process, the final and initial values of internal energy are the same, and the change in internal energy is zero.  U net = 0 and Q net = W ne t Chapter 10 Section 2 The First Law of Thermodynamics

Cyclic Processes, continued A heat engine uses heat to do mechanical work. A heat engine is able to do work (b) by transferring energy from a high-temperature substance (the boiler) at T h (a) to a substance at a lower temperature (the air around the engine) at T c (c). Chapter 10 Section 2 The First Law of Thermodynamics The internal-combustion engine found in most vehicles is an example of a heat engine.

Combustion Engines Chapter 10 Section 2 The First Law of Thermodynamics

The Steps of a Gasoline Engine Cycle Chapter 10 Section 2 The First Law of Thermodynamics

Refrigeration Chapter 10 Section 2 The First Law of Thermodynamics

The Steps of a Refrigeration Cycle Chapter 10 Section 2 The First Law of Thermodynamics

Objectives Recognize why the second law of thermodynamics requires two bodies at different temperatures for work to be done. Calculate the efficiency of a heat engine. Relate the disorder of a system to its ability to do work or transfer energy as heat. Section 3 The Second Law of Thermodynamics Chapter 10

Efficiency of Heat Engines The second law of thermodynamics can be stated as follows: No cyclic process that converts heat entirely into work is possible. As seen in the last section, W net = Q ne t = Q h – Q c . According to the second law of thermodynamics, W can never be equal to Q h in a cyclic process. In other words, some energy must always be transferred as heat to the system’s surroundings ( Q c > 0). Chapter 10 Section 3 The Second Law of Thermodynamics

Efficiency of Heat Engines, continued A measure of how well an engine operates is given by the engine’s efficiency (eff ). Chapter 10 Section 3 The Second Law of Thermodynamics Because of the second law of thermodynamics, the efficiency of a real engine is always less than 1.

Sample Problem Heat-Engine Efficiency Find the efficiency of a gasoline engine that, during one cycle, receives 204 J of energy from combustion and loses 153 J as heat to the exhaust. Chapter 10 Section 3 The Second Law of Thermodynamics 1. Define Given: Diagram: Q h = 204 J Q c = 153 J Unknown eff = ?

Sample Problem, continued 2. Plan Choose an equation or situation: The efficiency of a heat engine is the ratio of the work done by the engine to the energy transferred to it as heat. Chapter 10 Section 3 The Second Law of Thermodynamics

Sample Problem, continued 3. Calculate Substitute the values into the equation and solve: Chapter 10 Section 3 The Second Law of Thermodynamics 4. Evaluate Only 25 percent of the energy added as heat is used by the engine to do work. As expected, the efficiency is less than 1.0.

Entropy In thermodynamics, a system left to itself tends to go from a state with a very ordered set of energies to one in which there is less order. The measure of a system’s disorder or randomness is called the entropy of the system. The greater the entropy of a system is, the greater the system’s disorder. The entropy of a system tends to increase. Chapter 10 Section 3 The Second Law of Thermodynamics

Entropy, continued The second law of thermodynamics can also be expressed in terms of entropy change: The entropy of the universe increases in all natural processes. Chapter 10 Section 3 The Second Law of Thermodynamics

Energy Changes Produced by a Refrigerator Freezing Water Chapter 10 Section 3 The Second Law of Thermodynamics Because of the refrigerator’s less-than-perfect efficiency, the entropy of the outside air molecules increases more than the entropy of the freezing water decreases.

Entropy of the Universe Chapter 10 Section 3 The Second Law of Thermodynamics

Multiple Choice 1. If there is no change in the internal energy of a gas, even though energy is transferred to the gas as heat and work, what is the thermodynamic process that the gas undergoes called? A. adiabatic B. isothermal C. isovolumetric D. isobaric Standardized Test Prep Chapter 10

Multiple Choice, continued 2. To calculate the efficiency of a heat engine, which thermodynamic property does not need to be known? F. the energy transferred as heat to the engine G. the energy transferred as heat from the engine H. the change in the internal energy of the engine J. the work done by the engine Standardized Test Prep Chapter 10

3. In which of the following processes is no work done? A. Water is boiled in a pressure cooker. B. A refrigerator is used to freeze water. C. An automobile engine operates for several minutes. D. A tire is inflated with an air pump. Multiple Choice, continued Standardized Test Prep Chapter 10

4. A thermodynamic process occurs in which the entropy of a system decreases. From the second law of thermodynamics, what can you conclude about the entropy change of the environment? F. The entropy of the environment decreases. G. The entropy of the environment increases. H. The entropy of the environment remains unchanged. J. There is not enough information to state what happens to the environment’s entropy. Multiple Choice, continued Standardized Test Prep Chapter 10

Use the passage and diagrams to answer questions 5–8. A system consists of steam within the confines of a steam engine, whose cylinder and piston are shown in the figures below. Multiple Choice, continued Standardized Test Prep Chapter 10 5. Which of the figures describes a situation in which  U < 0, Q < 0, and W = 0? A. (a) B. (b) C. (c) D. (d)

Use the passage and diagrams to answer questions 5–8. A system consists of steam within the confines of a steam engine, whose cylinder and piston are shown in the figures below. Multiple Choice, continued Standardized Test Prep Chapter 10 6. Which of the figures describes a situation in which  U > 0, Q = 0, and W < 0? F. (a) G. (b) H. (c) J. (d)

Use the passage and diagrams to answer questions 5–8. A system consists of steam within the confines of a steam engine, whose cylinder and piston are shown in the figures below. Multiple Choice, continued Standardized Test Prep Chapter 10 7. Which of the figures describes a situation in which  U < 0, Q = 0, and W > 0? A. (a) B. (b) C. (c) D. (d)

Use the passage and diagrams to answer questions 5–8. A system consists of steam within the confines of a steam engine, whose cylinder and piston are shown in the figures below. Multiple Choice, continued Standardized Test Prep Chapter 10 8. Which of the figures describes a situation in which  U > 0, Q > 0, and W = 0? F. (a) G. (b) H. (c) J. (d)

9. A power plant has a power output of 1055 MW and operates with an efficiency of 0.330. Excess energy is carried away as heat from the plant to a nearby river. How much energy is transferred away from the power plant as heat? A. 0.348  10 9 J/s B. 0.520  10 9 J/s C. 0.707  10 9 J/s D. 2.14  10 9 J/s Multiple Choice, continued Standardized Test Prep Chapter 10

10. How much work must be done by air pumped into a tire if the tire’s volume increases from 0.031 m 3 to 0.041 m 3 and the net, constant pressure of the air is 300.0 kPa? F. 3.0  10 2 J G. 3.0  10 3 J H. 3.0  10 4 J J. 3.0  10 5 J Multiple Choice, continued Standardized Test Prep Chapter 10

Use the passage below to answer questions 11–12. An air conditioner is left running on a table in the middle of the room, so none of the air that passes through the air conditioner is transferred to outside the room. 11. Does passing air through the air conditioner affect the temperature of the room? (Ignore the thermal effects of the motor running the compressor.) Short Response Standardized Test Prep Chapter 10

Use the passage below to answer questions 11–12. An air conditioner is left running on a table in the middle of the room, so none of the air that passes through the air conditioner is transferred to outside the room. 11. Does passing air through the air conditioner affect the temperature of the room? (Ignore the thermal effects of the motor running the compressor.) Answer: No, because the energy removed from the cooled air is returned to the room. Short Response Standardized Test Prep Chapter 10

Use the passage below to answer questions 11–12. An air conditioner is left running on a table in the middle of the room, so none of the air that passes through the air conditioner is transferred to outside the room. 12. Taking the compressor motor into account, what would happen to the temperature of the room? Short Response, continued Standardized Test Prep Chapter 10

Use the passage below to answer questions 11–12. An air conditioner is left running on a table in the middle of the room, so none of the air that passes through the air conditioner is transferred to outside the room. 12. Taking the compressor motor into account, what would happen to the temperature of the room? Answer: The temperature increases. Short Response, continued Standardized Test Prep Chapter 10

13. If 1600 J of energy are transferred as heat to an engine and 1200 J are transferred as heat away from the engine to the surrounding air, what is the efficiency of the engine? Short Response, continued Standardized Test Prep Chapter 10

13. If 1600 J of energy are transferred as heat to an engine and 1200 J are transferred as heat away from the engine to the surrounding air, what is the efficiency of the engine? Answer: 0.25 Short Response, continued Standardized Test Prep Chapter 10

14. How do the temperature of combustion and the temperatures of coolant and exhaust affect the efficiency of automobile engines? Extended Response Standardized Test Prep Chapter 10

14. How do the temperature of combustion and the temperatures of coolant and exhaust affect the efficiency of automobile engines? Answer: The greater the temperature difference is, the greater is the amount of energy transferred as heat. For efficiency to increase, the heat transferred between the combustion reaction and the engine ( Q h ) should be made to increase, whereas the energy given up as waste heat to the coolant and exhaust ( Q c ) should be made to decrease. Extended Response Standardized Test Prep Chapter 10

Use the information below to answer questions 15–18. In each problem, show all of your work. A steam shovel raises 450.0 kg of dirt a vertical distance of 8.6 m. The steam shovel’s engine provides 2.00  10 5 J of energy as heat for the steam shovel to lift the dirt. Extended Response, continued Standardized Test Prep Chapter 10 15. How much work is done by the steam shovel in lifting the dirt?

Use the information below to answer questions 15–18. In each problem, show all of your work. A steam shovel raises 450.0 kg of dirt a vertical distance of 8.6 m. The steam shovel’s engine provides 2.00  10 5 J of energy as heat for the steam shovel to lift the dirt. Extended Response, continued Standardized Test Prep Chapter 10 15. How much work is done by the steam shovel in lifting the dirt? Answer: 3.8  10 4 J

Use the information below to answer questions 15–18. In each problem, show all of your work. A steam shovel raises 450.0 kg of dirt a vertical distance of 8.6 m. The steam shovel’s engine provides 2.00  10 5 J of energy as heat for the steam shovel to lift the dirt. Extended Response, continued Standardized Test Prep Chapter 10 16. What is the efficiency of the steam shovel?

Use the information below to answer questions 15–18. In each problem, show all of your work. A steam shovel raises 450.0 kg of dirt a vertical distance of 8.6 m. The steam shovel’s engine provides 2.00  10 5 J of energy as heat for the steam shovel to lift the dirt. Extended Response, continued Standardized Test Prep Chapter 10 16. What is the efficiency of the steam shovel? Answer: 0.19

Use the information below to answer questions 15–18. In each problem, show all of your work. A steam shovel raises 450.0 kg of dirt a vertical distance of 8.6 m. The steam shovel’s engine provides 2.00  10 5 J of energy as heat for the steam shovel to lift the dirt. Extended Response, continued Standardized Test Prep Chapter 10 17. Assuming there is no change in the internal energy of the steam shovel’s engine, how much energy is given up by the shovel as waste heat?

Use the information below to answer questions 15–18. In each problem, show all of your work. A steam shovel raises 450.0 kg of dirt a vertical distance of 8.6 m. The steam shovel’s engine provides 2.00  10 5 J of energy as heat for the steam shovel to lift the dirt. Extended Response, continued Standardized Test Prep Chapter 10 17. Assuming there is no change in the internal energy of the steam shovel’s engine, how much energy is given up by the shovel as waste heat? Answer: 1.62  10 5 J

Use the information below to answer questions 15–18. In each problem, show all of your work. A steam shovel raises 450.0 kg of dirt a vertical distance of 8.6 m. The steam shovel’s engine provides 2.00  10 5 J of energy as heat for the steam shovel to lift the dirt. Extended Response, continued Standardized Test Prep Chapter 10 18. Suppose the internal energy of the steam shovel’s engine increases by 5.0  10 3 J. How much energy is given up now as waste heat?

Use the information below to answer questions 15–18. In each problem, show all of your work. A steam shovel raises 450.0 kg of dirt a vertical distance of 8.6 m. The steam shovel’s engine provides 2.00  10 5 J of energy as heat for the steam shovel to lift the dirt. Extended Response, continued Standardized Test Prep Chapter 10 18. Suppose the internal energy of the steam shovel’s engine increases by 5.0  10 3 J. How much energy is given up now as waste heat? Answer: 1.57  10 5 J

19. One way to look at heat and work is to think of energy transferred as heat as a “disorganized” form of energy and energy transferred as work as an “ organized” form. Use this interpretation to show that the increased order obtained by freezing water is less than the total disorder that results from the freezer used to form the ice. Extended Response, continued Standardized Test Prep Chapter 10

19. One way to look at heat and work is to think of energy transferred as heat as a “disorganized” form of energy and energy transferred as work as an “ organized” form. Use this interpretation to show that the increased order obtained by freezing water is less than the total disorder that results from the freezer used to form the ice. Extended Response, continued Standardized Test Prep Chapter 10 Answer: Disorganized energy is removed from water to form ice, but a greater amount of organized energy must become disorganized to operate the freezer.

Entropy Chapter 10 Section 3 The Second Law of Thermodynamics

Energy Changes Produced by a Refrigerator Freezing Water Chapter 10 Section 3 The Second Law of Thermodynamics

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