Entropy- Introduction

The measure of disorganization

Entropy is a very important concept in physics and chemistry.

In our daily life we normally see that things , if left by themselves, get more and more disorganized. The opposite never happens. For instance, if you leave your earphones in some drawer, chances are that the lead will get entangled. You can leave it there for as long as you want, but it is very unlikely (almost impossible) that the lead will disentangle by itself. In fact, if you have other cables in the same drawer, chances are that you will end up with a big mess, as time goes by. I always found incredible how leads get entangled sponteaneously.The same phenomenon is observed in polymers, where long molecules get entangled, producing strong materials.

Another typical example is a cup that falls on the floor and breaks in hundreds of pieces. Will it ever get together again, by itself? Strictly speaking, there is a tiny possibility that the cup will go back up on the table, although it may sound absurd. It is all about probabilities.

If we saw a movie showing the cup going back up the table and getting back into one piece, we would (correctly) infer that it was a trick and the movie was being shown back to front.

That suggests that the arrow of time is determined by increasing entropy. This theory has been developed by Stephen Hawking.

I have produced an animation that illustrates that. It shows the mixing of two different gases, characterized by a red or blue colour. In this animation, they can be mixed slowly or more abruptly. In any case, they get more and more mixed up, as time goes by. You can wait as long as you want, and chances are that you won't be the gases separating back to the initial situation.


Living systems can self-organize, but inanimate matter can't (although crystal growing is some sort of self-organization).


Applications of the concept of entropy in chemistry>>



© Ricardo Esplugasde Oliveira - ricardochemistry@gmail.com