🚀 go-pugleaf

On Sep 20, 4:55 am, Pentcho Valev <pva...@yahoo.com> wrote:


The best way to violate the Second Law of Thermodynamics is to buy it
dinner, take it to a show, go out for drinks and dancing afterwards,
get it drunk, whisper sweat nothings into its ear, take it back to her
place, pull down her .... <good part left to your imagination>

> Take a suspended and stretched spring. It can lift a weight as it
> contracts, that is, we GAIN work. However, in order to restore the
> initial stretched state of the spring, we must SPEND work so there is
> no net gain. If both contraction and stretching are carried out in a
> reversible fashion, the net work gained at the end of the cycle is
> zero.

This example from the paper is on page 11017, top of the right column
(i.e, I actually read the paper).


"If". You don;t know that to be reversible,the contraction and
expansion must take place infinitesmally slowly.

>
> Consider again a suspended and stretched spring but this time it is
> "chemical", that is, we have one of the macroscopic contractile
> polymers described by Dan Urry in:

OK.

>
> http://pubs.acs.org/doi/abs/10.1021/jp972167t
> J. Phys. Chem. B, 1997, 101 (51), pp 11007 - 11028
> Dan W. Urry, "Physical Chemistry of Biological Free Energy
> Transduction As Demonstrated by Elastic Protein-Based Polymers"
>
> If, before contraction, we add acid (H+) to the system,

Right away, there is problem, since you no longer have a closed
system.

> the force of
> contraction and, respectively, the work gained as the polymer
> reversibly contracts increase. Then, just before stretching, we remove
> the added H+ from the system: the force of contraction and,
> respectively, the work spent as we reversibly stretch the polymer
> decrease. At the end of the cycle, THE NET WORK GAINED FROM
> CONTRACTION AND STRETCHING IS POSITIVE.

But you added WORK to the system; it took work to ADD the protons, and
it took work to REMOVE the protons.

>
> So far things go against the second law of thermodynamics

Only if you completely misunderstand the Second Law.

> but the
> complete account requires that the net work gained from adding H+ to
> and removing H+ from the system be evaluated. If it is positive or
> zero, the second law is definitively violated. If it is negative, the
> second law is saved for the moment.

"for the moment" Whew! That was close. "Missed it by THIS much."

> In the absence of the polymer, adding H+ to and removing the same
> amount of H+ from the system, in a reversible fashion, would amount to
> zero net work gained. The polymers designed by Urry, however, release H
> + as they contract, and absorb H+ as we stretch them. It is easy to
> see

For you, it is never easy enough, I'm afraid.

> (for people experienced in electrochemistry at least)

That certainly isn't you.

> that this
> makes the net work gained from reversibly adding H+ to and then
> removing the same amount of H+ from the system POSITIVE.

At best, the energy to add H+ might be made equal to the energy
required to remove H+, which would make the net work zero.
Practically, it takes energy both to add H+ and to remove it.

>
> Conclusion: The reversible cycle:
>
> 1. The polymer is stretched. We add H+ to the system.
> 2. The polymers contracts and lifts a weight.
> 3. We remove the same amount of H+ from the system.
> 4. We stretch the polymer and restore the initial state of the system.
>
> violates the second law of thermodynamics.

Wrong again.
In the paper itself, the authors analyze the thermodynamics of many
different transformations (it is a very cool paper, but not for the
reasons that Pentcho thinks) in terms of the Gibbs free energy.

The condition for equilibrium, Delta G =0, where Delta G = Delta H - T
Delta S, is just a restatement of the Second Law. If your freshamn
chemistry teacher did not show this derivation, go back and ask for
your tuition back. Or, go find a book and read it. It is in virtually
every freshman chem books, and ALL physical chemistry texts.


>
> Pentcho Valev

Pent-cho Valev? There are five of you?

> pva...@yahoo.com