Question

Does the entropy per cycle increase, decrease, or remain the same for (a) a Carnot refrigerator, (b) a real refrigerator, and (c) a perfect refrigerator (which is, of course, impossible to build)?

Short answer

1. For a Carnotrefrigerator, the entropy per cycleremains the same.
2. For a realrefrigerator, the entropy per cycle will increase.
3. For a perfect refrigerator, the entropy per cycle will decrease.

Step-by-step solution

The given data

1. A Carnot refrigerator
2. A real refrigerator
3. A perfect refrigerator

Understanding the concept of entropy change

Entropy change is a phenomenon that quantifies how disorder or randomness has changed in a thermodynamic system. From the processes followed by given refrigerators, we can decide about the entropy.

(a) Calculation of the entropy change of a Carnot refrigerator

A Carnot refrigerator is an ideal refrigerator. All processes are reversible and there is no wastage of energy due to friction and turbulence. The entropy per cycle remains the same for reversible processes.

Hence, entropy remains the same for a Carnot refrigerator.

(b) Calculation of the entropy change of a real refrigerator

A real refrigerator loses energy due to the friction. This is an irreversible process. Therefore, the entropy of this refrigerator increases.

(c) Calculation of the entropy change of a perfect refrigerator

A perfect refrigerator transfers heat energy from the cold reservoir to the hot reservoir. Therefore, the entropy of a perfect engine decreases, that is negative which violates the second law of thermodynamics.