Project ForgeProcess Calculations
Laws of Thermodynamics
GATE 2019
Medium
A rigid, perfectly insulated container is partitioned into two unequal parts by a thin membrane. One part contains one mole of an ideal gas at Pi, Ti while the other is evacuated. The membrane ruptures; the gas fills the entire volume and the equilibrium pressure is Pf=Pi/4. The change in molar entropy (Sf−Si) is
- ACp ln2 + R ln4
- B−Cv ln2 + R ln4
- R ln4
- DCp ln2
Explanation
Free (Joule) expansion into vacuum: adiabatic, no work done, so ΔU=0, and for an ideal gas this means ΔT=0 (isothermal). ΔS=R·ln(Vf/Vi)=R·ln(Pi/Pf)=R·ln4.
Source: GATE CH 2019 (2019)
This question is part of a 15-day revision cycle — sign in and Project Forge will bring it back the day before you'd forget it.