From: skroger@zeus.calpoly.edu (Seth L. Kroger)
Newsgroups: talk.origins
Subject: Re: Thermodynamics FAQ
Date: 25 Jul 92 01:00:12 GMT
Organization: California Polytechnic State University, San Luis Obispo


My Responce to Henley's Thermo: Part 1

I've writted up a response to Henley's Thermo FAQ (such that it is).
Due to the length of the post, I've decided to break it up into four
parts.

First off, his main premise seems to be to confuse everyone by
redefining what a "closed system" is.  Of course the 2nd Law of Thermo
uses the term "isolated system" but many people use the term "closed
system" as a synomyn.  With this in mind, he doesn't make much of any
point at all.

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.

henley@eng.auburn.edu (James Paul Henley) writes:
>o What is Thermodynamics?
>
>  "Thermodynamics is defined as the study of energy, its forms and
>   transformations, and the interactions of energy with matter." [1, p.5]
>
>Energy can exist in a number of forms, electrical energy, chemical energy,
>potential energy, kinetic energy, PV energy, mechanical energy, etc.  In
>order to apply the laws of thermodynamics mathematically, which is the
>only way to "prove" anything, you must have a definition of energy that
>is consistent with the laws of Thermo. The Laws of Thermo describe
>the Laws by which transformations in energy must abide.  They have never
>been shown false, and they have been demonstrated so thoroughly, that
>they are not considered theories, but laws.  The field of engineering
>is based largely on these laws, and in most fields of engineering*,
>proposed processes must first be shown to satisfy these laws to merit
>furthur consideration.  In chemical engineering, they are necessary criteria
>for chemical reaction equilibria.
>
>W : Work - Energy transfer due to a force acting against a resistance.  In
>           most general sense, work can be described as change.

Work is considered the transfer or change of organized energy. There
is zero entropy transfer when work is done.  It need not be against
some "resistance." If you drop an object on an airless moon, work has
been done but the object has encountered no resistance before it hits
the surface.  Also, in engineering the term resistance implies
irreversibility.  

>Q : Heat Transfer - one of three different types of energy transfer:
>   1) Conduction
>   2) Convection
>   3) Radiation

Heat transfer is the transfer of disorganized energy.

>[Enthalpy def. deleted]
>
>Gibbs energy is a measure of the amount of energy available to do work
>(ie. to effect a change) in chemical processes.  To determine Gibbs energy
>we take the enthalpy, and subtract out the disordered energy, ie. the energy
>that is not available to do work:
>
>G = H - TS
>
>G : Gibbs free energy
>S : entropy
>T : temperature
>
>So, what is entropy?
>
>Entropy is a measure of the disorder of the energy of a system.  Ordered
>energy is available to do work, disordered energy is not. So, mathematically
>we see that entropy*temperature is the amount of disordered energy at that
>temperature.

No.  Entropy is the degree of microscopic disorganization, our
uncertainty of the about the microscopic state.  [1, p.  166] Let's
say you have some gas at a certian temperature and pressure.  There
are many microscopic states the atoms can be in that will produce this
state.  Some states of pressure and temperature will have more
possible corresponding microstates than others.  These states will
have the higher entropy.

It deals with the states of particles, not necessarily just the states
of energy.

Also, you haven't shown that entropy*temperature is the amount of
disordered energy.  You just thew up a bunch of symbols and made a
statement without any backup for it.

>One criterion for chemical equilibruim in a closed system is that the total
>Gibbs free enery must be at a minimum, which means that entropy must be at a
>maximum.

>[1] _Fundamentals_of_Engineering_Thermodynamics_, Howell and Buckius,
>McGraw-Hill, 1987
>[2] _Introduction_to_Chemical_Engineering_Thermodynamics_, _Fourth_Edition_,
>Smith and van Ness, McGraw-Hill, 1987
>[3] _Classical_Thermodynamics_of_Nonelectrolyte_Solutions_, van Ness and
>Abbott,  McGraw-Hill, 1982
>
>
>James P. Henley Jr.
>Chemical Engineering Dept.
>Auburn University

[1] Renyolds, William C., and Perkins, Henry C., _Engineering_
    _Thermodynamics_, 2nd ed., McGraw-Hill, 1977.

|======================================================================|
| Seth Kroger                                                          |
| skroger@pan.calpoly.edu                                              |
| Cal Poly, San Luis Obispo                                            |
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