Re: [Phys-L] heat content

["Bob Sciamanda" <treborsci@verizon.net>]

I guess I must notice-->
JD writes:

"In the «final» state of the system, or any other state, you
cannot distinguish the «thermal energy» from any other kind
of energy.  We're talking about an undefined and undefinable
thing, so it doesn't matter what you call it."

Is it not possible, and useful, to distinguish that part of the system 
energy which has been "thermalized" - that energy which directly affects the 
system temperature and phase?


-----Original Message----- 
From: John Denker
Sent: Monday, February 10, 2014 10:57 PM
To: Phys-L@Phys-L.org
Subject: Re: [Phys-L] heat content

On 02/10/2014 06:44 PM, Bob Sciamanda wrote:

>   dE = - P dV + T dS  "
>
> JD seems to want to restrict the discussion to the use of the term
> "thermal energy" to the mechanism by which energy is TRANSPORTED.
> Others see the term as applicable to the role of the final energy
> CONTENT of the system, however it was acquired.

Rather than comment on that directly, let me just say in my
own words what I want to say:

1) If the subject is «the term "thermal energy"» that's not
what I'm talking about.  I don't care about the term.

As I have said many times:  Ideas are primary and fundamental.
Terminology is tertiary.  Terminology is important only insofar
as it helps us formulate and communicate ideas.

In the literature, there are long-running holy wars about the
definition of "heat" and "thermal energy".  I have repeatedly
and emphatically said I am not interested.  I recognize four
or five different mutually-inconsistent technical definitions
of "heat", each of which has some advantages and disadvantages,
and I refuse to fight about it.

2) If we are talking about the /idea/ of "thermal energy", then
we agree that I am *not* using that term -- or any other term --
to talk about the «final energy CONTENT» of the system.

If others want to use the term in this way, we have a problem,
not because of the term, but because of the idea.

In the «final» state of the system, or any other state, you
cannot distinguish the «thermal energy» from any other kind
of energy.  We're talking about an undefined and undefinable
thing, so it doesn't matter what you call it.

3) Given not just a «mechanism» but a detailed process, including
a specific path through thermodynamic state space, you can (if
you want) calculate the integral of T dS.  The result exists, but
it is *not* a function of state (except maybe in trivial cases).
It is a /functional/ of the path, depending on every detail of
the path.

As for the term "thermal energy", I don't care whether you apply
it to this integral, or to something else, or both, or neither.

As for the physical thing represented by this integral, I don't
care whether you call it "thermal energy" or "heat" or "caloric"
or something else or all of the above or none of the above.

No matter what the name, ∫ T dS is what it is, and it is *not* a
function of state.  A lot of people wish it were a function of
state, but wishing does not make it so (except maybe in trivial
cases).

4) If you want to get picky, I'm not necessarily talking about
anything being «TRANSPORTED».  Loosely speaking, dS represents
the change in S.  This change may or may not involve transport.
If we restrict attention to reversible processes, then dS is
always associated with transport, but this is not the general
case.

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Bob Sciamanda
Physics, Edinboro Univ of PA (Em)
treborsci@verizon.net
http://sciamanda.com