Thermodynamics

7-1

Chapter 7 ENTROPY

Entropy and the Increase of Entropy Principle

7-1C No. The

∫ δ Q represents the net heat transfer during a cycle, which could be positive.

7-2C No. A system may produce more (or less) work than it receives during a cycle. A steam power plant, for example, produces more work than it receives during a cycle, the difference being the net work output. 7-3C The entropy change will be the same for both cases since entropy is a property and it has a fixed value at a fixed state. 7-4C No. In general, that integral will have a different value for different processes. However, it will have the same value for all reversible processes. 7-5C Yes. 7-6C That integral should be performed along a reversible path to determine the entropy change. 7-7C No. An isothermal process can be irreversible. Example: A system that involves paddle-wheel work while losing an equivalent amount of heat. 7-8C The value of this integral is always larger for reversible processes. 7-9C No. Because the entropy of the surrounding air increases even more during that process, making the total entropy change positive. 7-10C It is possible to create entropy, but it is not possible to destroy it. 7-11C If the system undergoes a reversible process, the entropy of the system cannot change without a heat transfer. Otherwise, the entropy must increase since there are no offsetting entropy changes associated with reservoirs exchanging heat with the system.

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7-2

7-12C The claim that work will not change the entropy of a fluid passing through an adiabatic steady-flow system with a single inlet and outlet is true only if the process is also reversible. Since no real process is reversible, there will be an entropy increase in the fluid during the...