Re: phase diagrams, partial pressure, etc.

["John S. Denker" <jsd@MONMOUTH.COM>]

Robert Cohen wrote:
> > > pressure of the substance at equilibrium, no?)

Then I wrote:
> > P means pressure.  I don't see what's confusing about that.

Well, contrary to my earlier thoughts (sorry!), I suspect this
_is_ a source of confusion.  In particular, on the phase
diagram P denotes the pressure of _the substance_ by itself,
or in more complicated situations the !!partial!! pressure
of that substance.

...
> and I'll ask some other students the following question:
>
> The air pressure in the room is 1 atm.  The temperature is 20C.  Which
> phases of water can exist in the room? Choose all that apply.
> A. Solid
> B. Liquid
> C. Gas
>
> Would this be sufficient to evaluate the validity of my concern?

Point taken.  Yes, I predict you'll catch a bunch who can't
recognize the difference between
        Ptotal = 1atm
and
        Ppartial = 10 torr of water.

PS to avoid unnecessary confusion, you might want to clarify
the question:
 -- phases that exist in equilibrium?
 -- phases that exist temporarily, out of equilibrium?