alleryStart learning →For the **isothermal free expansion** of an ideal gas into vacuum, which set of statements is correct?
- q > 0, w < 0, ΔU > 0
- q = 0, w = 0, ΔU = 0
- q < 0, w > 0, ΔU = 0
- q = 0, w > 0, ΔU > 0
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Correct answer: B. q = 0, w = 0, ΔU = 0
Free expansion occurs against zero external pressure, so $w = -p_{ex}\Delta V = 0$.
Joule's experiment showed that for an ideal gas, expansion into vacuum produces no temperature change, so $q = 0$.
From the first law, $\Delta U = q + w = 0$.
Internal energy of an ideal gas depends only on T, which is unchanged here, confirming ΔU = 0.