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A rigid, thermally-insulated tank undergoes stirring as shown in the figure below. Which one of the following options is correct?

1. The enthalpy of the air increases while the entropy of the air remains constant
2. Both the enthalpy and the entropy of the air remain constant
3. Both the enthalpy and the entropy of the air increase
4. The enthalpy of the air decreases while the entropy of the air increases

Correct answer: Both the enthalpy and the entropy of the air increase

Solution

Stirring the air in a thermally-insulated tank introduces mechanical energy into the system, which increases both the enthalpy due to the added energy and the entropy as the air molecules become more disordered.

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