Entropy : Chaotic Systems

[V]

Hey, I was wondering if any of you understand chemistry enough to explain to me how Entropy works in more simplified terms. I've been trying to research it myself for some time but it seems like there's a lot of explanations where the author has too much background information to explain so they try to work around it which makes the explanation vague.

Knowledge for Knowledge's sake. Can you help me out?

[Oliver]

I'm about to go and do a Chemistry degree next year, so I might be able to help.

What I understand of entropy so far is self taught, but I can give you my understanding of its consequences for chemical reactions. Entropy seems to be lots of different concepts depending on what area you're considering it in.

The practical approach is to define entropy as energy added to or removed from a system, divided by the mean absolute temperature over which the change takes place.

The more theoretical side of it is something like this, but as I said, it's self taught at the moment, as I haven't covered it at school yet ^^ Here are some definitions of Entropy:

The concept of entropy can be described qualitatively as a measure of energy dispersal at a specific temperature.

Entropy is a measure of the disorder or randomness of a system.
- Something with a high entropy is very disorganized, something with a low entropy is very organized.

Reactions happen because it is almost always favourable energetically, and as a result there is a change in enthalpy in reactions. In exothermic reactions, energy is given out overall, and in endothermic, energy is taken in overall. Entropy may act against or with this change.

All reactions are spontaneous to some degree under the right conditions or amount of time, and spontaneous changes are always accompanied by a dispersal of energy - so with some reactions this dispersal of energy has an effect on the overal energy change. This disperal of energy is entropy.

Entropy can act in opposition to the normal enthalpy change of a reaction, as nature favours randomness and disorder as well as lower energy states. This is evidenced by the experimental difference in energy changes that are measured when compared to the theoretical calculations based on enthalpy alone.

Ice melting is entropy increasing - the disorder of the arrangement of the molecules increases.

Entropy increases in the overall system in the same direction as time flows.

Wikipedia has a nice section on its relevance to chemistry, and specifically with Chemical Thermodynamics, the following can be said:

The second law of thermodynamics states that entropy in the combination of a system and its surroundings (or in an isolated system by itself) increases during all spontaneous chemical and physical processes. Spontaneity in chemistry means “by itself, or without any outside influence”, and has nothing to do with speed.

Entropy is equally essential in predicting the extent of complex chemical reactions, i.e. whether a process will go as written or proceed in the opposite direction. For such applications, ΔS must be incorporated in an expression that includes both the system and its surroundings, ΔS(universe) = ΔS(surroundings) + ΔS(system). This expression becomes, via some steps, the Gibbs free energy equation for reactants and products in the system: ΔG [the Gibbs free energy change of the system] = ΔH [the enthalpy change] −T ΔS [the entropy change].


I have to say it's a really difficult concept to get your head around, and I don't understand it properly yet ^^

But the overall idea to take away is that entropy acts to create an equilibrium between order and disorder, because otherwise every chemical reaction would increase order so much we'd have no disorder and life wouldn't function - so eventually everything in the universe will be in equilibrium and nothing more can happen - that's the 'heat death theory' of the universe.

Oh dear this is horrible. I'm sorry. I'm going to read more on this now. I'll post it in case it helps, but I shall work with you to grasp this better! =p

[Oliver]

Enjoy! =D