"Floyd L. Davidson" wrote in message ...
"Larry Brasfield" wrote:
"Tom MacIntyre" wrote in
message ...
On Wed, 15 Jun 2005 18:01:25 -0500, John Fields
wrote:

On Tue, 14 Jun 2005 11:21:21 -0800, (Floyd L.
Davidson) wrote:

The idea that water boils at 100C and freezes at 0C, without
some mention of pressure, has little meaning. Water can "boil"
at 0C too.

Not true, unless 0.01+ oC counts as "0C" or "boil" has
some novel meaning other than a liquid to vapor phase
transition occuring within the liquid due to applied heat.

Since, by your own admission, the boiling and freezing point
temperatures of water are pressure dependent, I invite you to state
what pressure would be required to be exerted on a volume of liquid
water in order to cause it to boil at 0°C.

[Stuff on latent heat zapped.]

I am simply
going by memory of my old Physics classes, and I have no idea what
pressure would be required to allow water to boil at 0 C. I think
other substances have boiled at lower temperatures than that at STP
though.

If you peruse the phase space of water at
http://www.lsbu.ac.uk/water/phase.html
you will see that there is no liquid/vapor boundary
at 0 oC. At a range of pressure well below standard
atmospheric, it could happen near 0.01 oC.

John's challenge is a bit of a trick and appears
to show he knows how to read that graph and
accompanying table.

Are you saying that it could happen at 0.01C but not at 0.00C,
because you see something in that chart which says water is liquid
at 0.01C and not at 0.00C?

I said "near 0.01 oC", not "at". At temperatures above
the triple point (at 0.01 oC), a liquid/vapor phase change
exists. Below that, there is no such phase change, so
there is no possibility of boiling, which requires a liquid.
Precisely at the triple point, I'm not sure it is meaningful
to speak of boiling because the triple point exists under
equilibrium conditions and boiling is not an equilibrium.
(Boiling is a catastrophic process.)

I don't see that in the chart at all. The chart does not have
sufficient resolution. It doesn't discuss that in the text
either.

The table of triple points shows, in its first row, that triple
point often referred to as "the triple point". (That is the one
now used to define 0.01 oC on the Centrigrade temperature
scale.) This triple point, between the liquid, Ih (hexagonal
ice-one) and vapor phases, represents the lowest pressure
at which an Ih/liquid phase transition exists, as can be seen
from the graph. It is clear from the graph that the vapor
phase boundary slope is continuous as it passes thru that
triple point, and has positive slope. So, clearly, where it
passes thru 0 oC has to be below that triple point.

Did you mean something else?

Nope.

--
--Larry Brasfield
email:
Above views may belong only to me.