HW-CH209th Edition CH20 Problems: 8, 28, 43, 45, 618th Edition CH20 Problems: 12, 34, 41, 45, 758.At very low temperatures, the molar speci°c heatCvof many solids is approximatelyCv=AT3,where A depends on the particular substance.For aluminum, A =3:15°10°5J=mol±K4. Findthe entropy change for 4.00 mol of aluminumwhen its temperature is raised from 5.00 K to10.0 K.28.In the °rst stage of a two-stage Carnot engine,energy is absorbed as heat Q1at temperatureT1, work W1is done, and energy is expelled asheat Q2at a lower temperature T2. The secondstage absorbs that energy as heat Q2, does workW2, and expels energy as heat Q3at a still lowertemperature T3Prove that the e¢ ciency of theengine is(T1²T2)=T1.43.Figure 20-32 represents a Carnot engine thatworks between temperaturesT1= 400KandT2= 150Kand drives a Carnot refrigerator thatworks betweenT3= 325K
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