Partial pressures really only applicable to gas mixtures. e.g. The partial pressure of Oxygen in the air is around 21.3kPa and the partial pressure of Nitrogen is around 80kPa.

It's probably something to do with hydrogen bonding. That always seemed to be the reason that water does strange things. The other regions are probably some sort of esoteric states of matter that have little relevance in the real world although I have little experience in dealing with them so don't take what I say as gospel.

but the answers to all your questions are there

except the almost vertical line doesn't give enough detail on the variation of freezing point with pressure 🙁

Joe Satriani did a great song called Ice 9…

I'll see if I can find the detail about the freezing point with pressure, I've got a text book around here somewhere with all this in..

Don't worry a real physicist will be along in a minute, I'm just a lowly materials engineer with a cursory grasp of what is going on..

It's probably something to do with hydrogen bonding.

yes, water is a paradoxical substance, and many of its characteristics are highly unusual.

I'm not sure that there are ever atmopheric conditions on earth where this would happen – for example the pressure on Everest is approx 30Kpa (sea level its 101kPa) which is above the sublimation pressure shown on the phase diagram.

It does all the time. If you fill an ice tray and leave it in the freezer for months, the cubes will get smaller. Meat gets "freezer burnt" after a few months, because the H2O molecules leave the meat, drying it out. It didn't pass through the liquid phaseon the way.

And depth hoar in a snowpack is formed by recrystalisation of sublimated water vapour.

Edit: toys, Just realised that we're not quite taking about the same thing: The graph shows that at certain pressures and temperatures, changes in one will provoke a change in state of all the material from solid straight to gas, and I think I was talking about common or garden entropy, in the form of sublimation.

I think.

nedrapier – I think I can explain this as there may be local convection currents so any flow across a surface will create very low pressure on that surface.

At low pressures the concept of Solid/liquid/gas is a bit difficult to define as the state is dependant on having other molecules nearby to interact with. If you have a very low pressure (like near or total vacuum) and introduce a single molecule of water at the sublimation temperature then is it a solid or gas? It's a bit of semantics, in reality the words we use to define solid/liquid/gas are generalisations…

nedrapier just seen your edit. Common or garden entropy is, I think, driven by local variations, at least this is what I remember…

I think we are on dodgy ground anyway as this is difficult to prove because you cannot observe exactly what happens at the surface without changing what happens (uncertainty principle).

just ask hainey

Simon Barnes.
Scroll down on that link, the next graph has what you are looking for.

ok we've done this now

can you explain the Mpemba effect now please 🙂

local variations was how I understood "natural" sublimation and evaporation works. water vapour leaves the surface of water all the time, the mloecules are jiggling about and every now and then the engery from combined jiggles is anough to overcome the surface tension (molecular attraction). The more energy there is in the water, the hotter it gets and the more often molecules are pinged out of the surface tension.

This happes too in ice, just less often, as there is less energy and less movement of molecules.

edit. just being silly.

i'll take that as a no 😆

yes, water is a paradoxical substance, and many of its characteristics are highly unusual…

It always makes me snigger when people say things like that – surely the characteristics of water are only unusual for something that isn't water.

The only paradox (about it) is that people think that 'our' theories of how matter behaves are little more than approximations based on idealised systems…….

gonefishin – Member
I'm pretty sure that SFB is correct. When you ski and snowboard you are actually riding on liquid water, not snow. This layer of water is probably no more than a few hundred molecules thick but it is liquid none the less. It's the reason that when it's really cold (-30/-40C) that snow become sticky as the pressure that it applied by you isn't enough melt the extremely cold snow.

NO

I did my dissertation on this, we concluded that yes there is a thin layer of water, but this is due to friction not pressure, as a by product of this we could make dry slopes feel like fresh powder!

Unfortunately we couldn't get a manufacturer to incorperate it as they believed it was destined for the same fate as those swiming suits, everyone is 2% faster in the olympics one year, they'r banned the next.

just reading about it now.

I like the opening story:

Origin

The effect is named for the Tanzanian high-school student Erasto B. Mpemba. Mpemba first encountered the phenomenon in 1963 in Form 3 of Magamba Secondary School, Tanzania when freezing hot ice cream mix in cookery classes and noticing that they froze before cold mixes. After passing his O-level examinations, he became a student at Mkwawa Secondary (formerly High) School, Iringa, Tanzania. The headmaster invited Dr. Denis G. Osborne from the University College in Dar Es Salaam to give a lecture on physics. After the lecture, Erasto Mpemba asked him the question "If you take two similar containers with equal volumes of water, one at 35 °C (95 °F) and the other at 100 °C (212 °F), and put them into a freezer, the one that started at 100 °C (212 °F) freezes first. Why?" only to be ridiculed by his classmates and teacher. After initial consternation, Dr. Osborne experimented on the issue back at his workplace and confirmed Erasto's finding. They published the results together in 1969.[2][3] As of 2002 Erasto Mpemba is retiring from being Principal Game Officer for the African Forestry and Wildlife Commission.[4]

yup, it's a great story

can you explain the Mpemba effect now please

isn't it a combination of solute precipitation and heat transfer being proportional to the temperature gradient ??

Didn't know that was called the Mpemba effect but the wikipedia link alludes to that fact that it is unproven…

Was told by an A level physics teacher (called Streaky Bonehead) that hot water cooled faster than cold water due to increased potential.

Now since then I've done lots of thermodynamics and what I do know is that the rate of heat transfer is proportional to the difference in temperature. So water at 100C in a freezer has a very large difference in temp, compared with tap water at say 20c, so the hot water will lose heat much faster than the tap water. The only problem with this is that as the 100c water cools then its rate of heat transfer reduces, so at 20C the rate of heat transfer is the same as the water that started at 20c. And the water that started at 20 c will be much colder than 20 c by now…

There is another good article about it here.

Nedrapier – your explanation of local variations suits my world view exactly. 🙂

So what tyres are needed for riding on Ice-5 then? ;o)

You'll need to prove whether the moon is made of cheese first before anything else according to the wonder kids on here! 😉

What would happen of course is that the pressure within the container
would increase by many powers of 10, but assume the container is strong
enough not to break. At first, if you kept the temperature at exactly 273.15 K (0 C.) the water would remain a liquid because the freezing point of icedecreases slightly with increasing pressure. However, when the pressure reached pressures of the order of 10^8 to 10^9 Pa., ice having a structure different than "normal" ice would form. Ice has at least seven different crystal structures depending upon the temperature and pressure.

catch up tankslapper 🙄

🙄 late developer….. 😆

Ice-9. That's the substance created by the naive scientist in Kurt Vonnegut's book Cat's Cradle. The one that "freezes" the planet when it escapes from it's container. Very cool book.

Say you fill a strong water proof safe with water then take it to well below freezing – does the water stay liquid as long as the safe doesn't break?

Is the OP actually an overcomplicated attempt at safe-breaking?

You'd be better off with a decent still saw and a blowtorch 😀

*** WARNING CAT'S CRADLE BOOK SPOILER ****

I recall that the motivation for ice-9 was a general who wanted a method of freezing mud to stop his tanks getting bogged down. To solve the problem, the naive scientist created a stable configuration of ice but at normal temperatures (ice-9). It turned water it made contacted with into more ice-9.

Utter disaster when someone tips it in the ocean and all the water on the planet becomes ice-9!

***********************************************