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Chapter 12 The Laws of Thermodynamics Quick Quizzes 1. (b). The work done on a gas during a thermodynamic process is the negative of the area under the curve on a PV diagram. Processes in which the volume decreases do positive work on the gas, while processes in which the volume increases do negative work on the gas. The work done on the gas in each of the four processes shown is: , W , W , and Thus, the correct ranking (from most negative to most positive) is a,c,b,d. 5 4.00 10 J a W = 5 3.00 10 J b = + 5 3.00 10 J c = 5 4.00 10 J d W = + 2. A is isovolumetric, B is adiabatic, C is isothermal, D is isobaric. 3. (c). The highest theoretical efficiency of an engine is the Carnot efficiency given by 1 c c e T = h T . Hence, the theoretically possible efficiencies of the given engines are: A 700 K 1 1000 K e = = .300 , B 500 K 1 0.375 800 K e = = , and C 300 K 1 600 K e = = .500 and the correct ranking (from highest to lowest) is C, B, A. 4. (b). r Q S T = = and Q in an adiabatic process. If the process was reversible, but not adiabatic, the entropy of the system could undergo a non-zero change. However, in that case, the entropy of the systems surroundings would undergo a change of equal magnitude but opposite sign, and the total change of entropy in the universe would be zero. If the process was irreversible, the total entropy of the universe would increase. = 5. The number 7 is the most probable outcome because there are six ways this could occur: 1-6, 2-5, 3-4, 4-3, 5-2, and 6-1. The numbers 2 and 12 are the least probable because they could only occur one way each: either 1-1, or 6-6. Thus, you are six times more likely to throw a 7 than a 2 or 12. 431 432 CHAPTER 12 Answers to Even Numbered Conceptual Questions 2. Either statement can be considered an instructive analogy. We choose to take the first view. All processes require energy, either as energy content or as energy input. The kinetic energy which it possessed at its formation continues to make Earth go around. Energy released by nuclear reactions in the core of the Sun drives weather on Earth and essentially all processes in the biosphere. The energy intensity of sunlight controls how lush a forest or jungle can be and how warm a planet is. Continuous energy input is not required for the motion of the planet. Continuous energy input is required for life because energy tends to be continuously degraded, as energy is transferred by heat into lower- temperature sinks. The continuously increasing entropy of the Universe is the index to energy-transfers completed. 4. Shaking opens up spaces between the jelly beans. The smaller ones have a chance of falling down into spaces below them. The accumulation of larger ones on top and smaller ones on the bottom implies an increase in order and a decrease in one contribution to the total entropy. However, the second law is not violated and the total entropy of the system increases. The increase in the internal energy of the system comes from the work required increases.... View Full Document
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