When a gas of n moles expands into twice the volume the entropy changes by ∆S = nRln2 (R is the universal gas constant NAkB). You should have addressed this in second year ? Now let’s say we have two different gases of 1 mole each on either side of a partition in a volume, as in the figure below. Each half only contains one kind of gas. When the partition is removed, discuss with some calculations how likely the gases will remain as is (separated), or mix into the total volume. [Hint: Call the number of microstates in the separated state Ωb and in the mixed state Ωa. What do you know about the relation between probability and microstates ?]