Which state function remains constant during a Joule-Thomson expansion of a real gas through an insulated porous plug?
Answer and explanation
Correct answer: D. Enthalpy (H)
- Step 1: A Joule-Thomson expansion is an adiabatic throttling process: Q = 0. Step 2. Work done on gas upstream = P1 V1; work done by gas downstream = P2 V2. Step 3. Net First Law: U2 - U1 = P1V1 - P2V2 => U1 + P1V1 = U2 + P2V2 => H1 = H2. The process is isenthalpic (constant enthalpy). Answer: Enthalpy (H). Why not the others: It is irreversible (entropy increases); internal energy changes as PV changes.
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