11. A refrigerator extracts 1200 J of heat energy from the cold reservoir and ex

Question

11. A refrigerator extracts 1200 J of heat energy from the cold reservoir and expels 1600 J of heat energy to the hot reservoir during each cycle. The temperature of the hot reservoir is 305 K and the temperature of the cold reservoir is 275 K.

a. Determine the work that must be done on the system during each cycle.

b. Determine the coefficient of performance of the refrigerator.

c. Determine the maximum coefficient of performance for a refrigerator operating between these two temperatures.

d. Does the entropy of the cold reservoir increase, decrease, or stay the same during each cycle?

e. Does the entropy of the hot reservoir increase, decrease, or stay the same during each cycle?

f. Does the total entropy of the universe increase, decrease, or stay the same during each cycle?

Explanation / Answer

a) W= | QH|-|QL| = 1600J-1200J = 400J

b) KC=|QL|/|QH|-|QL| = 1200J/400J= 3

c) KC=|TL|/|TH|-|TL| = 275/(305-275) = 9.17

d)(-QL)/TL = -1200J/275K= - 4.364 J/K

e) QH/TH = 1600J/305K = 5.246 J/K

f) S= (-QL)/TL - QH/TH = -4.364+5.246 = 0.882 J/K

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