5. Entropy of Reversible Mixing of Ideal Gases. What is the change in entropy, ΔmixS, associated with mixing two ideal gases of different kinds (│ and ●) reversibly? This can be accomplished in a special container with two semi-permeable pistons that each only allow only one type of gas to pass through, as shown, that can be slowly moved apart. The number of │ molecules is N│ and the number of ● molecules is N●. The volumes of their initial containers are V1 and V2, and P1 = P2 = Pf, as shown.
Solve using classical thermodynamics, not statistical thermodynamics in this case.
Initial State
V1, P1
V2, P2
Final State
Vf = V1 + V2, Pf
piston permeable only to │
piston permeable only to â—Ź
**Hint: compare the work done by each gas on the opposite respective piston as the pistons are moved apart (and recall the thermodynamic definition of entropy). Each gas can only perform reversible PV-type work on the piston which it cannot diffuse through. The temperature of the container is held constant, so the change in internal energy is also constant throughout this process (these are ideal gases).