How is entropy related to osmosis and diffusion?

1 Answer
Aug 13, 2018


Well, what is #"entropy"#?


#"Entropy"# can be defined as the statistical probability for disorder. It is certainly a measurable property, and has units of #J*mol*K^-1#. And entropy is the fundamental driving force for ALL physical and chemical change...all systems tend towards maximum entropy, maximum disorder as the preferred state.

And so, should we have TWO solutions separated by a semipermeable membrane, there is a statistical driving force towards the state of maximum disorder, and least DIFFERENCE in concentration. The SOLVENT moves in a direction to equilibrate the concentration, such that there is net movement from the LESS concentrated side of the membrane to the MORE concentrated...i.e. movement from weaker to stronger concentration expresses the osmotic potential. And so we could say that the process of #"osmosis"# is entropy-driven....

And remove the membrane, or even consider TWO cylinders of DIFFERENT gases connected by a valve. Turn open the valve and certainly there is no violation of the principle of conservation of energy should the gas molecules REMAIN in their source bottles. And yet entropy demands maximum disorder, maximum microstates, such that the individual gaseous particles become mixed...i.e. diffusion is entropy driven.

And recall the old Boltzmann definition of entropy....

#S=k_Blog{Omega}#...where #k_B="Boltzmann's constant"#, and #Omega="the number of microstates..."#

Anyway, I think you should have a good read of your text, and lecture notes...(and I will do the same thing before I shoot my mouth off again!)….