Chemistry - Thermodynamics - I Question with Solution | TestHub
A portion of helium gas in a vertical cylindrical container is in thermodynamic equilibrium with the surroundings. The gas is confined by a movable heavy piston. The piston is slowly pushed down by a distance H from its equilibrium position and then kept in that position long enough for thermodynamic equilibrium to be re-established. After that, the container is insulated and then the piston is released. After the piston comes to rest, what is the new equilibrium position of the piston with respect to the initial position?
Options:
Answer:
Solution:
Let the initial column height be L and the constant pressure (atmosphere plus piston weight) be P, so nRT0 = PLA. After the slow isothermal push the column is (L - H) at T0. On release the gas expands irreversibly and adiabatically against constant P to final pressure P. 1.5(PV2 - PLA) = -P(V2 - (L-H)A), so 2.5V2 = (2.5L - H)A and V2 = (L - 0.4H)A. The piston ends 0.4H below its initial position. Matches (c).
