Re: what is the relation between force and energy?

From: Old Man (nomail_at_nomail.net)
Date: 09/21/04 

Date: Tue, 21 Sep 2004 17:20:41 -0500

"Bjoern Feuerbacher" <feuerbac@thphys.uni-heidelberg.de> wrote in message
news:cipc8p$nnu$2@news.urz.uni-heidelberg.de...
> yogesh wrote:
> >>No. Why do you think so? Pressure has the same units as energy/volume.
> >>But pressure is not the same as energy density!
> >
> > IN thermodynamics while calculating the enthaply(i.e the total energy
> > content) of a system we consider pressure-volume energy also..
> > H = U + PV.(i.e internal energy + pressure volume energy)
> >
> > Now definitely here, the pressure is considered as a energy density.
>
> Hum, yes, something like that. But your claim was:
> "But if I know the pressure ( or if I can calculate the pressure from
> the forces) then certainly I know the energy/volume of the system."
>
> The formula H = U + pV does not support that claim in any way!
>
> Bye,
> Bjoern

In H = U + PV, What is included in U ?

1) Kinetic energy of molecular rotation and internal vibrations ?
2) Potential energy of interactions between gas molecules ?

It would seem that 2) would be included in the pressure, P.

Estimating the vapor pressure of a solution via molecular
 number density is approximate, possibly because solute
ionization isn't complete and the effect of that on the
electric dipole moment of the water molecule. Is there
a concise explanation for the rather large deviations from
empirical determination ?

As a physicist, it's humiliating to resort to tables in the
"Handbook of Chemistry & Physics" rather than to
calculate it outright, especially when many organic solutes
aren't listed.

Usually clear and concise, Landau & Lifshitz in "Statistical
Mechanics" aren't at all clear on this subject.

[Old Man]