Engineering Board Exam Reviewer · Thermodynamics · easy

The free (unrestrained) expansion of an ideal gas into a vacuum in an insulated rigid vessel results in:

1. An increase in temperature
2. A decrease in temperature
3. A decrease in entropy
4. No change in internal energy and temperature

Answer

D. No change in internal energy and temperature

Solution

Q = 0 and W = 0, so U = 0; for an ideal gas T stays constant. The process is irreversible, so entropy increases.

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