5.15. In the figure is shown the cycle for a Carnot refrigerator. This cycle is

Question

5.15. In the figure is shown the cycle for a Carnot refrigerator. This cycle is the same as the
Carnot engine except that the direction along each path is reversed. Paths A and C are
adiabatic (Q = 0), and paths B and D are isothermal (T = 0). Consider the working
substance of this refrigerator to be an ideal gas. Fill in the chart below as in the previous
problem. Now, using your completed chart, answer the following question. Is the work
done on the gas along path B positive, negative, or zero? You only get one try answering
this question.

5.16. In the previous problem, is the change in internal energy of the gas along path C
positive, negative, or zero? You only get one try answering this question.
5.17. In the previous problem, is the heat put into the gas along path D positive, negative, or
zero? You only get one try answering this question.
5.18. In the previous problem, is the change in internal energy the gas along path D positive,
negative, or zero? You only get one try answering this question.
5.19. In the previous problem, is the net work done on the gas during the entire cycle positive,
negative, or zero? You only get one try answering this question.
5.20. In the previous problem, is the net change in internal energy of the gas during the entire
cycle positive, negative, or zero?

Explanation / Answer

15) since dV>0, W is positive

16) adiabatic so Q = 0

du= Q + W

and W<0 since dV<0

so dU<0

17) since isothermal dU = 0

so Q + W = 0

since dV<0, W<0
so Q>0 so positive

18) since isoterm, dU = 0

19)since area is ccw, dW<0 so negative

20) since you come back to the same place, dU = 0
so zero

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