An ideal gas initially at equilibrium doubles its volume at temperature by two…
PHYSICS · Single correct · AP · Physics 2: Algebra-based · Thermodynamics · Thermodynamics
Problem
An ideal gas initially at equilibrium doubles its volume at temperature T by two different methods.
Process X: The gas expands slowly and reversibly while in thermal contact with a large reservoir at temperature T.
Process Y: The gas undergoes a rapid free expansion into a vacuum inside an insulated container.
Which of the following best explains why the total entropy change of the universe is greater for Process Y than for Process X?
(a) Process X is carried out very slowly, and the prolonged motion creates additional friction and turbulence that generate more microscopic disorder, so its entropy contribution to the universe exceeds that of Process Y.
(b) Process Y involves no heat exchange, so the surroundings cannot supply the negative entropy needed to offset the gas’s positive entropy change.
(c) In Process X, heat leaves the gas and is absorbed by the reservoir at a slightly lower effective temperature, so the same amount of heat produces a larger entropy increase in the surroundings than in Process Y.
(d) During the free expansion in Process Y the gas cools, lowering its own entropy relative to Process X, so the universe’s total entropy rise is smaller.