For an adiabatic free expansion of an ideal gas into an evacuated vessel (vacuum), which of the following sets of thermodynamic parameters is correct?

Answer and explanation

Correct answer: B.

  1. Step 1: In an adiabatic process, there is no heat exchange with the surroundings, so .
  2. Step 2: During free expansion against vacuum (), no work is done against opposing force, so .
  3. Step 3: Applying the first law . Since for an ideal gas, as well.
Answer
.
Why not the others: incorrectly assumes heat absorption during expansion; confuses free expansion with expansion against an external pressure; assumes heat is released to vacuum.

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