Two identical monatomic gases are separated by an insulating partition inside a rigid…
PHYSICS · Single correct · A Level · Physics · Further mechanics and thermal physics · Further mechanics and thermal physics
Problem
Two identical monatomic gases are separated by an insulating partition inside a rigid container. Gas A is at 600 K and gas B is at 300 K. Immediately after the partition is removed, the gases begin to mix.
Which of the following microscopic descriptions best predicts how the speed distributions of the gases change in the first moments after contact and explains why?
(a) Both speed distributions instantaneously become identical, centered at a speed corresponding to the average of 600K and 300K, because mixing immediately creates thermal equilibrium.
(b) Molecules from gas A rapidly lose kinetic energy and the peak of their speed distribution shifts to lower speeds, primarily because they undergo frequent collisions with the slower molecules of gas B.
(c) Molecules from gas A gain kinetic energy while those from gas B lose kinetic energy, so both peaks move in opposite directions, because collisions favor transfer from slow to fast molecules.
(d) The peaks of both speed distributions shift to lower speeds because collisions convert kinetic energy into potential energy within the gas, reducing the overall temperature of the mixture.