Re: Is it at all possible -- at least in theory -- to violate the

On Fri, 12 Oct 2007 13:26:59 -0400, "Perplexed in Peoria"
<jimmenegay@xxxxxxxxxxxxx> wrote:


"J. J. Lodder" <nospam@xxxxxxxxxxxxxxxx> wrote in message news:1i5vrt7.wtizvk1p9eiwjN@xxxxxxxxxxxxxxxxxxxx
Perplexed in Peoria <jimmenegay@xxxxxxxxxxxxx> wrote:

"J. J. Lodder" <nospam@xxxxxxxxxxxxxxxx> wrote in message news:1i5v615.1x98bf4
k3fgaN@xxxxxxxxxxxxxxxxxxxx
Rich Townsend <rhdt@xxxxxxxxxxxxxxxxxxx> wrote:

J. J. Lodder wrote:
Rich Townsend <rhdt@xxxxxxxxxxxxxxxxxxx> wrote:

J. J. Lodder wrote:
Green Xenon [Radium] <glucegen1@xxxxxxxxxx> wrote:

Hi:

Is it theoretically possible to successfully perform an activity that
violates the second law of thermodynamics?
No, none whatsoever.
Not true. The 2LOT only applies to large ensembles. For a
sufficiently-small ensemble of atoms, violation of the 2nd law occurs
quite frequently.

Nonsense.
You misunderstand the second law.
What it says is that it is impossible
to create a perpetuum mobile of the second kind.
(just as the first law says that you can't build
a perpetuum mobile of the first kind)

And that holds absolutely, no exceptions,


No, that's a *consequence* of the second law. The law itself says nothing
about perpetual motion machines, it simply states that the entropy of a
closed system cannot decrease.

Perhaps in your book, but not in most good thermodynamics textbooks.
On the contrary, concepts like absolute temperature and entropy
are derived as necessary consequences of the second law.
(you skipped that tedious chapter on reversible heat enguines?)
And finally, after having introduced these concepts
non-decrease of entropy in closed systems can be derived
as a consequence.

Without having the second law first
you can't even know what entropy is.

As I understand it, you don't need the whole 2nd law. All you need is the
idea that two systems in thermal contact will eventually become isothermal.
This is sometimes called the Zeroth Law. Then you define dS=dQ/T,
claim (or does it require proof?) that S is a state function, and you are set
up to postulate the 2LoT.

Without the second law you don't know what T is.

Not according to this:
http://en.wikipedia.org/wiki/Zeroth_law

And yes, that requires proof,

That S, as defined above, is a state function? It seems to me that it is a
state function by definition. But I may be missing some subtlety. In any
case, the statistical mechanics 'Boltzmann' definition of entropy that
Townsend provided clearly doesn't need the 2LoT for its definition.

You seem to have some strange ideas about thermodynamics. It might save
some time if you adopted a less 'oracular' stance and offered some
justification or explanation for your rather cryptic statements. There are
some people here who know thermo pretty well, and it is my impression
that you are disagreeing with them pretty freely.

By purest chance (no doubt a complete reversal of entropy?) I happen
to have open on my lap as I type a book titled "Thermodynamics"
written by someone named Enrico Fermi, who might just know a thing or
two about the subject.

Chapter 1 is about thermodynamic systems and state conditions and
deals with variables of pressure, volume, and temperature. Without
those three you cannot discuss the notion of equation of state for a
perfect gas. At this time, Fermi writes: "We define T provisionally
as the temperature indicated by a gas thermometer in which the
thermometric gas is kept at a constant low pressure. T is then
proportional to the volume of the gas. We shall see later, however
[after discussion of the 2nd law but before introduction of entropy] ,
that it is possible to define this same scale of temperatures T by
general thermodynamic considerations..." (p. 8, Dover Publications,
1936).

Chapter 2 is about the first law. Chapter 3 is about the second law
without any mention of the notion of entropy. Herein lie the two
statements I already cited in a previous post about the second law,
one by Kelvin about not being able to convert heat to work in an
isothermal system, the other by Clausius about not being able to move
heat from a lower to a higher temperature. Fermi gets around the
notion of temperature by restating the Clausius law as follows: "If
heat flows by conduction from a body A to another body B, then a
transformation whose only final result is to transfer heart from B to
A is impossible." (p. 31). In that way, the temporary introduction
of temperature in chapter 1 is bypassed. Fermi then introduces the
Carnot cycle and then defines thermodynamic temperature in terms of
heat exchanges in the Carnot cycle first using the temporary
"empirical" temperature defined in Chapter 1 then dispensing with the
empirical definition by showing it to fall out. The result: "The
temperature scale which we have just defined is called the
_absolute_scale_of_temperature_ [italics in the original]. It has
the advantage of being independent of the special properties of any
thermodynamic substance.... We shall now show that the absolute
thermodynamic temperature coincides with the absolute temperature T
introduced [in Chapter 1] with the aid of a gas thermometer." (pp.
41-42).

In other words, thermodynamic temperature is defined as a consequence
of the second law. Entropy is not introduced until Chapter 4. The
second law precedes both notions.

As to the distinction between classical thermodynamics and statistical
thermodynamics, Fermi first discusses the historical basis of the laws
of "pure" (i.e. classical) thermodynamics as predating the idea that
heat is a form of energy. Even back in the days when heat was a
"fluid" (before 1842 when Mayer showed the equivalence of heat and
mechanical work and made possible the first law), Carnot in 1824 was
able to show the limitations of transforming heat into work producing
what was essentially the second law. (Paraphrasing from p. ix).

Fermi then goes on to say

"We know today that the actual basis for the equivalence of heat and
dynamical energy is to be sought in the kinetic interpretation, which
reduces all thermal phenomena to the disordered motions of atoms and
molecules....This branch of mechanics, called _statistical_mechanics_,
which has been developed mainly through the work of Maxwell,
Boltzmann, and Gibbs, has led to a very satisfactory understanding of
the fundamental thermodynamic laws"

" But the approach in pure thermodynamics is different. Here the
fundamental laws are assumed as postulates based on experimental
evidence, and conclusions are drawn from them without entering into
the kinetic mechanism of the phenomena. This procedure has the
advantage of being independent, to a great extent, of the simplifying
assumptions that are often made in statistical mechanical
considerations. Thus, thermodynamic results are generally highly
accurate." (pp. ix - x).

.

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