Classical thermodynamics make no mention of 'disorder'. The second law of thermodynamics is an experimental result, and has two statements (I quote from the notes written by my professor):
Clausius' statement:' There can not exist a thermodynamical system whose only effect, if undergoing a cycle, is to extract work from a system and communicate the same amount of work to another system at a higher temperature.'
Kelvin-Plank statement:' There is not exist a thermodynamical ststem whose only effect, if undergoing a cycle, is to extract heat from a certain system and do the same amount of work on another.'
These two statements can be proven to be equivalent within the framework of thermodynamics. But as I said, there is no mention of disorder. In fact, there is no mention of entropy. The idea of entropy is a later development derived from Clausius' theorem, which in turn is derived from the second law, but I suppose the statement of the second law you wrote down is sometimes used instead of the two above because entropy is a theoretical concept obtained from the second law.
At least they way I was taught it ( this is science, I could have been taught wrong, but I hope not), entropy hasn't the slightest thing to do with disorder,or at least, as I've said before, in the context of classical Thermodynamics. That doesn't make it any less important though, maybe just less interesting to the rookie student or the layman. Entroy is a thermoydamic potential and a function of state. That means that it is a function only of the configuration of the system in every given moment, not how to system came to be in that way: if c_1 and c_2 are to different curves in the thermodynamic space of the system, then:
S=S(T,a_1,a_2,...) ; ΔS = \int _{c_1}dS=\int _{c_2}dS
At first sight it might not seem to significant, but it is. The principle of minimum entropy will tell you how a system will evolve, and when it will stop, and that is so deep that it more or less gives us our sense of time.
I have been quite extense, but with a point: no, in thermodynamics there is no concept of disorder. It is a later development of statistical physics. The use of your statement of the second law could be ( and is, I believe) misleading, especially if you are a layman or a second year student like myself. That may be the origin of the ambiguity you have observed. In any case, the second law of thermodynamics, and it's consequences, deserve a lot more thought than anyone can probably afford to give them.
Hope I have been helpful. This is my first proper response.
Haborix said:
In my experience with learning thermodynamics I have found that instructors try very hard to avoid, when they first introduce the subject, the word "disorder"
You should have come to our college. If anyone even tried to steer the lecture towards disorder, our professor would stop whoever it was and put them back into context. He didn't mention or let anyone mention disorder once! And he still made it clear that Entropy is as important as anything could get.
