From: skroger@zeus.calpoly.edu (Seth L. Kroger)
Newsgroups: talk.origins
Subject: Re: Thermodynamics FAQ
Date: 28 Jul 92 19:49:29 GMT
Organization: California Polytechnic State University, San Luis Obispo

henley@eng.auburn.edu (James Paul Henley) writes:
>In article <1992Jul25.010012.154199@zeus.calpoly.edu> skroger@zeus.calpoly.edu (Seth L. Kroger) writes:
>
>I am going to address this point now, even though I will cover it in detail
>later.  I was confused about why everyone kept saying that an open system
>was an isolated system.  Maybe only engineers make the distinction.  So
>I got out my Physical Chemistry textbook and looked it up to see how Chemists
>define a closed system.  This is what I found:
>
>  "An isolated system is one that does not interact in any way with its
>   surroundings.  Changes in the surroundings cannot result in any changes
>   in the isolated system.  Neither matter nor energy can pass across the
>   boundaries of on isolated system.  Systems that are completely isolated
>   from the rest of the universe do not really exist, but as limiting
>   concepts they are often used in thermodynamic discussions."
>
>  "A closed system is one in which there is no transfer of matter across the
>   boundaries between system and surroundings.  The mass of a closed system
>   remains constant.  Note that a closed system can still interact with its
>   surroundings in many other ways, for example by compression or expansion,
>   by transfers of energy.  *A CLOSED SYSTEM IS BY NO MEANS ISOLATED*."

Perhaps.  The fact still remains that "closed system" = "isolated system" in
common usage.  You just threw out a new definition without explaining
whether the common definition is incorrect/imprecise.  Your premise that
people falsely call the earth a closed system is wrong, because you
don't take the common definition in consideration.

Considering that t.o isn't a technical group, I would argue that the common
definition of a closed system holds here (although isolated would be
better).


>_Basic_Physical_Chemistry_, Walter J. Moore, Prentice Hall, 1983, page 7.
>
>Now I have found the same definition of closed and isolated systems in
>every thermodynamics book that I have looked at, and also in a Physical
>Chemistry Book.  For the life of me I cannot figure out how I can be accused
>of redefining the meanings.  It appears to me that some other people around
>here are doing the redefining, not me.

The Thermo books I've looked at only define "isolated systems."

>>Second, his writing style here unclear and confusing in general.
>>His FAQ reads like many bad lectures I've had where you have no idea
>>that the instructor is talking about, and you have no idea where the
>>things he's talking about are coming from.  He makes statements
>>without backing them up and throws out terms without explaining them.
>
>This is rich, really rich.  So far, I have only seen one other reference
>mentioned, and *IT DID NOT CONTRADICT WHAT I SAID*.  Yet I have seen
>many statements by members of t.o that contratradicted what I said, and
>none of them are backed up by references.  I thought it was only creationists
>that did that kind of thing.

Here I was harping on the writing style of your post, not your content.  You
threw up a bunch of equations with very little explanation, some of which
had no particular bearing on the post.  An entire week is spent explaining
the control volume equation in thermo class, and you just pop it in and
expect people to understand it.  You threw out several terms without
explaining them (for example enthalpy and extensive).

Since it is intended to be a FAQ, I feel that a much better job should be
done.  Many readers probably don't have much of a technical background in
the area.  Such a FAQ should be written more clearly.

>James P. Henley Jr.

Hmm. Hacked on my general summaries and not my specifics, ehh.


|======================================================================|
| Seth Kroger                       "If God made us in His image we    |
| skroger@pan.calpoly.edu               have certianly returned the    |
| Cal Poly, San Luis Obispo             complement."  -Voltaire        |
Newsgroups: talk.origins,sci.astro