• Question: Please may you describe entrapy for me?

    Asked by elliop to Clare, Mariana, Pedro, Robert, Susanne on 14 Nov 2012.
    • Photo: Susanne Muekusch

      Susanne Muekusch answered on 14 Nov 2012:

      Hi elliop,

      sorry, entropy is just a mess 😉 I don’t think I can explain it.

      Seriously, thermodynamics and me are not compatible. I know that entropy is a measure of the order (or rather disorder) of the molecules or atoms in a system. And it always increases, to lower the entropy (disorder) of a system, energy is required. I remember the professor talking about his desk in that context, where the default direction is towards more entropy (chaos) and you need energy to counteract. That’s thermodynamic nonsense, but a nice metaphor.

      That’s it. Maybe someone else here remembers his/her physics lectures better.
      Why do you want to know? Where did you come across entropy?

    • Photo: Clare Taylor

      Clare Taylor answered on 14 Nov 2012:

      elliop – I am loving your questions! They are really making me think, and also taking me back to my school days and physics lessons!

      People often describe entropy as the tendency of an isolated system to move towards disorder, or chaos. But what does that actually mean? I’ll try and explain! Entropy is a measure of the second law of thermodynamics (do you know that one?) that says that energy within a system will spread out if nothings stops it. Entropy is a measure of the spontaneousness of the spread of that energy (I think!).

      I’ll try and give you an example to illustrate: Why do ice cubes melt?

      Say leave an ice cube in the sink to melt, think about the energy and molecules involved. The ice cube is cold, so the water molecules are moving slowly. If the sink is warmer, its molecules will be moving faster. These faster molecules will have a tendency to disperse their energy by making the slower moving molecules in the ice cube speed up i.e. get warmer and cause the ice to melt. This follows the second law of thermodynamics and should be a spontaneous process involving an increase in entropy in the ice as it melts to form water. At the same time, the sink decreases in entropy as it gives up some energy to the ice cube.

      So you see, nothing about disorder or chaos there! But did that make sense to you?!

    • Photo: Mariana Campos

      Mariana Campos answered on 14 Nov 2012:

      The simplest way to describe it would be..Entropy is the level of disorder in a system, and in each system it tends to increase: meaning that a system tends to more chaos. It actually applies to my bedroom and my desk: it tends to be more and more chaotic with time 😉
      This is as far as my thermodinamics go. But Susanne and Clare have very nice answers 😉

    • Photo: Robert Insall

      Robert Insall answered on 15 Nov 2012:

      I used to have a chemistry teacher who demonstrated entropy. He took a new beaker, and threw it on the floor, and smashed it to bits. Then he collected up the bits, and asked if he threw them down on the floor if they would form into a new beaker?

      The answer is of course no – there are so many different ways of being smashed into bits, and only one way of being intact, so the chances of the beaker reforming are nothing. The smashed bits are “high entropy” and the intact beaker is “low entropy”.

Comments