ism_ch18

# ism_ch18 - Chapter 18 The Laws of Thermodynamics Answers to...

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381 Chapter 18 The Laws of Thermodynamics Answers to Even-numbered Conceptual Questions 2. From Equation 18-3, we can see that 300 J of heat must be added to this system. 4. (a) Yes. Heat can flow into the system if at the same time the system expands, as in an isothermal expansion of a gas. (b) Yes. Heat can flow out of the system if at the same time the system is compressed, as in an isothermal compression of a gas. 6. No. The heat might be added to a gas undergoing an isothermal expansion. In this case, there is no change in the temperature. 8. Yes. In an isothermal expansion, all the heat added to the system to keep its temperature constant appears as work done by the system. 10. The final temperature of an ideal gas in this situation is T ; that is, there is no change in temperature. The reason is that as the gas expands into the vacuum is does no work – it has nothing to push against. The gas is also insulated, so no heat can flow into or out of the system. It follows that the internal energy of the gas is unchanged, which means that its temperature is unchanged as well. 12. This would be a violation of the second law of thermodynamics, which states that heat always flows from a high-temperature object to a low-temperature object. If heat were to flow spontaneously between objects of equal temperature, the result would be objects at different temperatures. These objects could then be used to run a heat engine until they were again at the same temperature, after which the process could be repeated indefinitely. 14. The work done from A to B is negative; the work done from B to C is positive; the work done from C to A is negative. 16. Yes, this would be possible. The problem is that you would need low-temperature reservoirs of ever lower temperature to keep the process going. 18. In principle, less energy would be required if the kitchen is cooler. The reason is that in this case the heat extracted from the water can be expelled at a lower temperature, which means that less work must be done by the refrigerator’s engine. 20. The entropy of the universe will increase if you rub your hands together, as in all frictional processes. 22. Assuming a reversible, adiabatic expansion, there will be no increase in entropy because there is no heat exchange. 24. The law of thermodynamics most pertinent to this situation is the second law, which states that physical processes move in the direction of increasing disorder. To decrease the disorder in one region of space requires work to be done, and a larger increase in disorder in another region of space.

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Chapter 18: The Laws of Thermodynamics Physics: An Introduction Solutions to Problems 1. 5 5 4.1 10 J 6.7 10 J Q W =− × 55 4.1 10 J 6.7 10 J 10.8 10 J UQW ∆=− = − × =− × 5 2. 3 2 3J 1210 J (1mol) 8.31 (276K 272K) 2m o l k 1160 J WQ U Qn R T    = 3. (a) 77 J ( 42 J) 119 J = (b) 77 J 42 J 35 J = (c) 120 J 120 J 0 QUW =∆ + + = 4.
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ism_ch18 - Chapter 18 The Laws of Thermodynamics Answers to...

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