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Unformatted text preview: HW-CH20
9th Edition CH20 Problems: 8, 28, 43, 45, 61 8th Edition CH20 Problems: 12, 34, 41, 45, 75
8. At very low temperatures, the molar speci...c heat 61. An inventor has built an engine X and claims that its e ciency "X is greater than the e Cv of many solids is approximately Cv = AT 3 , ciency " of an ideal engine operating between where A depends on the particular substance. the same two temperatures. Suppose you couFor aluminum, A = 3:15 10 5 J=mol K 4 . Find ple engine X to an ideal refrigerator (Fig. 20the entropy change for 4.00 mol of aluminum 35a) and adjust the cycle of engine X so that the when its temperature is raised from 5.00 K to work per cycle it provides equals the work per 10.0 K. cycle required by the ideal refrigerator. Treat 28. In the ...rst stage of a two-stage Carnot engine, this combination as a single unit and show that energy is absorbed as heat Q1 at temperature if the inventor' claim were true(if "X > "), the s T1 , work W1 is done, and energy is expelled as combined unit would act as a perfect refrigerheat Q2 at a lower temperature T2 . The second ator (Fig.20-35b), transferring energy as heat stage absorbs that energy as heat Q2 , does work from the low-temperature reservoir to the highW2 , and expels energy as heat Q3 at a still lower temperature reservoir without the need for work. temperature T3 Prove that the e ciency of the engine is (T1 T2 )=T1 . 43. Figure 20-32 represents a Carnot engine that works between temperatures T1 = 400K and T2 = 150K and drives a Carnot refrigerator that works between T3 = 325K and T4 = 225K. What is the ratio Q3 =Q1 ? 45. Construct a table like Table 20-1 for eight molecules. 1 ...
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- Spring '11