Re: latent heat of evaporation

[Bernard Cleyet <anngeorg@PACBELL.NET>]

I suspect the temperature at which the evap. takes place affects the
value mightily.  e.g. at the appropriate critical point it's zero.  That
doesn't mean somewhere 540 wasn't required to reach the CP.  JD's  ?
about conservation of E., I suspect applies here.  If I remember
correctly, this is discussed in the elementary text I met back in the
early 60's.  (Sears?)

bc, who remembers heat lamps are very useful when evaporating
radioactive solns.

p.s.  I suspect that more energy is required to create a bubble at the
bottom of a deep ocean and then L is correspondingly greater *,
however, I suspect the p is included in the definition of L, e.g. at one
atm and 100 deg. etc. L is 540.

* I suspect this all may be in the std. steam tables.

Ludwik Kowalski wrote:

> As far as i know no bubbles are formed when evaporation takes place
> without boiling, for example at 90 C. Molecules
> escape from a flat surface overcoming surface tension forces. That is
> when, I suppose, the value of 540 cal/g is valid.  This topic is new to
> me. I do not know what to expect when bubbles are formed. Should L
> become larger or should it become smaller than 540? Perhaps someone
> will supply the answer based on thermodynamics. Or on laboratory data.
> I am sure that the topic has been studied in the past.
> Ludwik Kowalski
>
>
> On Sunday, Sep 26, 2004, at 19:47 America/New_York, Herbert H Gottlieb
> wrote:
>
>
>
> > I really do not fully understand your reply.
> > Don't bubbles always form below the surface???
> > Under what conditions would you expect the
> > bubbles to be formed elsewhere?
> >
> > Herb   :-)
> >
> >
> > On Sun, 26 Sep 2004 14:44:31 -0400 Ludwik Kowalski
> > <kowalskil@MAIL.MONTCLAIR.EDU> writes:
> >
> >
> > > I suppose that latent heat of evaporation of water,
> > > L=540 cal/gm, applies to evaporation from the
> > > surface (to overcome attractive molecular forces).
> > > What evidence can be found that L remains the
> > > same during intensive boiling? I am watching a
> > > heating resistor immersed in a beaker. In this
> > > case most bubbles are formed below the
> > > surface, near the heating coil.
> > > Ludwik Kowalski
> > Herb Gottlieb from New York City
> > A friendly  place to live and visit