Re: atmospheric pressures

On Mon, 10 Jul 2006 20:39:34 -0500, Math Freak wrote:

On 10 Jul 2006 01:28:51 -0700, tadchem wrote:

Math Freak wrote:

It represents a phase change by changing the temperature while keeping
the pressure constant.

"Changing the temperature while keeping the pressure constant" is a
thermodynamic process


I'm talking about traversing across the areas on phase-diagram, not
conducting an experiment, Bozo.

Following a line across the areas of a phase-diagram would be conducting
an experiment, or at least a thought-experiment.

Water phase has some interesting quirks:

http://www.lsbu.ac.uk/water/phase.html

Interestingly, I'm not seeing an ice IV, a material hypothesized in _They
Shall Have Stars_ by James Blish and used to build a bridge on Jupiter for
confirming a certain equation that led to the spindizzy. Perhaps that got
mutated into Ice XI, or just left out to avoid confusion.

Also, apparently ice sublimes directly below about 10^3 Pascal, not unlike
carbon dioxide here on Earth.

So...say one starts out at 600 K, 1 GPa, then heats the water keeping the
temperature constant to, say, 700K. One then reduces the pressure to 100
MPa, then reduces the temperature to 600 K again, then increases the
pressure back to 1 GPa. This defines a square loop on this pressure
diagram, where about 1/3 of it is clearly liquid, but about 2/3 of it is
superfluid. However, the boundary between liquid and superfluid is very
very fuzzy, at least on this diagram.

Contrast that to the square loop defined by 400K, 1 MPa, and 500K, 100
kPa, or 300K, 100 kPa and 400K, 10 kPa. Presumably the former is easily
enough done in many pressure cookers, since 1 atm = 102325 Pa. The latter
might be done in a vacuum distillation apparatus.

The second graph, which is merely redrawing part of the first graph using
linear instead of log pressure, shows possibilities which are already
realized by such things as an ice skater's blade. Clearly, below -20C
(14F) ice skaters will have a very difficult time of it, unless one
explicitly heats the blade, which is admittedly possible because of
friction but said friction would also slow down the skater.

I'll also admit to some confusion as to the heat of fusion; presumably,
the ice skater's blade has to expend some energy to melt the water,
cooling the blade and the water slightly. The water later refreezes,
heating the ice in its vicinity after the skater has passed.



- isochoric heating/cooling. There is only a phase change if the
material being studied changes phase.




"isochronic was not found in the Cambridge advanced
Learner's Dictionary

Did you spell it correctly? Here are some alternatives:

* icecream"

http://dictionary.reference.com/search?q=isochoric

3 entries found for _isochoric_.

(Physics) A line upon a thermodynamic diagram so drawn as to represent the
pressures corresponding to changes of temperature when the volume of the
gas operated on is constant.

http://dictionary.reference.com/search?q=isochronic

1 entry found for _isochronic_.

(isochronal)

[rest snipped]

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