My teacher constantly stresses that 10 moles of a gas going to 11 moles of a gas will ALWAYS cause an increase in entropy (ΔS>0). But why? For example (I know that O2 shouldn't technically be a liquid, but just as an example): 2H2O(g)⇔H2O(g)+(3/2)O2(l)+2H2 It seems iffy to me. We go from 2mol(g)↔1mol(g), BUT we also have 2moles⇔(7/2)moles. Is the moles of gas rule just a "it usually works" kind of rule, or is it a tried-and-true physics fact? Thanks so much!