Re: Lowest energy level and increase in enthropy

["RAUBER, JOEL" <JOEL_RAUBER@SDSTATE.EDU>]

Too add a footnote to what David is saying:

It is probably better to say that "things have a tendency to increase their
entropy" (when considered as an isolated entity);  rather than saying

"> >We learn that things have a tendency to go to their lowest energy
> > levels."

Often this corresponds to a tendency to head towards lowest energy levels
but not always.  The "not always" is important enough that I wish students
never learned the phrase "things have a tendency to go to their lowest
energy
levels."

Why does an electron in an excited hydrogen atom decay to its ground state
and give off a photon?  I'd not answer that the system seeks a state of
lowest energy; but rather that the state of electron in ground state with
photon flying off is entropically favored compared to the excited state (or
indeed other excited states).

Joel Rauber

> -----Original Message-----
> From: David Bowman [mailto:David_Bowman@GEORGETOWNCOLLEGE.EDU]
> Sent: Monday, February 26, 2001 10:34 AM
> To: PHYS-L@lists.nau.edu
> Subject: Re: Lowest energy level and increase in enthropy
>
>
> Regarding the question of K Alexakos:
>
> > While covering the 2nd law of thermodynamics one of my students asked
> > the following question which I still can't answer properly
> in my mind:
> > We learn that things have a tendency to go to their lowest energy
> > levels.
>
> But this is not necessarily the case.  The 'tendency' of
> 'things' in any
> circumstance is to do what they tend to do in *that* circumstance.
> Although this observation *is* quite tautological, it is
> often overlooked
> by many who are confused by the 2nd law.
>
> It is only true that a 'thing' tends to go to its lowest energy levels
> when the 'thing''s surroundings are sufficiently cool so that if the
> 'thing' preferentially occupied those lowest levels, it would have the
> same temperature as those surroundings.  If the 'thing''s surroundings
> are hotter than the 'thing', then the 'tendency' is for the 'thing' to
> go to *higher* energy levels than it currently tends to occupy.  The
> 'tendency' is *not* necessarily to go from high energy to low energy,
> but rather, to go in such a way as to tend to equalize the temperature
> of the 'thing' with that of the surroundings.
>
> > How does this reconcile with the fact that entropy in the
> > universe is increasing?
>
> The correct 'tendency' is *quite* well reconciled with this principle.
> When the energy of 'things' tends to be exchanged with their
> environment in such a way as to bring about a reduction in the
> temperature difference between the things and the environment, *that
> does* 'tend' to increase the entropy of the universe.
>
> > Am I missing something simple?
>
> It appears that what is missing is an understanding of 'things' really
> 'tend' to do.  (I don't know if an understanding of the meaning of
> the increase of entropy in the universe is missing or not because it
> was not elaborated on in the question enough to find out.)
>
> David Bowman