Category Archives: Thermodynamics

Explaining Entropy can be a mess…


Another scientific concept that is hard to grasp by laypeople and that to my opinion has been the center of much distortion in the chemistry classroom, is the thermodynamical function Entropy, S.

More often than not, S is said to be a measure of “disorder” and people just take it! If one was to define disorder then one would have to also define order: Is my apartment too entropic? what about my life? Does nature understand order in the same way as we do? How do we understand order inside a living cell where many molecules and organelles are floating around? If indeed S was a measure of disorder then, why is it important to measure it?

Entropy in a nutshell. There have been many attempts to define S in a way young students may understand it, yet tracing parallelisms with ordinary every-day-life concepts is hard and often leads to miss conceptions.  A student of mine once asked: “if entropy is always increasing, how come bodies tend to cool down?” he meant to ask how come the translation motions of a molecular ensamble tended to decrease (and with this achieving “order”.)

Prof. Mayo Martínez-Kahn at UNAM in Mexico wrote a very interesting paper about Entropy in the local journal of the Chemistry School, “Educación Química”. The paper was entitled “The tombs of Entropy” as a reference to the widely known fact that in Boltzmann’s tomb his famous equation relating Entropy to the partition function Q, is engraved. Prof. Martínez then ventures in imagining how would other tombs from people who have made contributions to the concept and notion of S would look like. I remember distinctively the one of Sadi Carnot’s in which his famous thermodynamic cycle was displayed.

Entropy in so many words is a function that describes how many different energy levels are available in a thermodynamic system. The more levels, the higher the entropy. It also describes the spontaneity of a process to occur since in nature a system always tends to undergo changes that increase its entropy along with that of its surroundings.

How come Gibbs’ free energy or Helmholtz don’t cause such confusions? my guess is because nobody has attached an every-day-word to them!

PS. It is still important to make scientific concepts permeate into the general audience. Recently decesead comedian George Carlin mentioned Entropy in the following video…

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