Vapor Pressure of Water
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- čas přidán 13. 06. 2010
- Water at room temperature will boil when the surrounding air pressure drops below the vapor pressure. In this case the vapor pressure is about 20 mmHg (20 Torr). Eventually we see the water freeze.
This video has been edited. The total time for the water to go from room temperature to freezing was about 90 seconds.
The pump was actually running when we poured the liquid nitrogen into the cold trap.
Sorry about the inconsistent lighting.
thanks for demonstrating
Thank you for this helpful demonstration.
Hi, Thom--
Thanks again.
Water has to be cold to freeze; that doesn't change very much with pressure.
One way to look at it is that the energy to boil at reduced pressure comes from the water itself. See watch?v=pOYgdQp4euc for an example.
Another way to look at it is that the water molecules that leave the beaker first are the fastest moving, or hottest molecules. Those left behind are slower/colder, and eventually are cold enough to freeze. Best regards.
Hi your 9 year old comment helped me understand this video. 9 years ago was 2012... Crazzyyy! So thanks mr extractables from 9 years ago!
That is pretty insane... the water was almost simultaniously boiling and freezing
BUT, what is the temperature of the frozen water. Come on guys. It's important to show that.
should the container be in closed system while boiling /?
getting my head round this, whilst the term "boiling" is applied to bubbling waters in such atmospheric conditions {we have NO heat} so here is my question, when we see this freeze and ice, Is there a temperature change showing freezing ?.
Thom in Scotland. {good videos guys}
Boiling is defined in terms of vapour pressure, i.e. the sudden vaporisation of water at the temperature when the vapour pressure of water equals the atmospheric pressure. Usually, we increase the temperature to increase the vapour pressure to boil, but here, conversely, they decrease the atmospheric pressure to equate it to vapour pressure and hence boil water. Btw vapour pressure is the pressure on the surface of the water in a closed container when the evaporation and condensation are in dynamic equilibrium.
Similarly, freezing is when the vapour pressure in liquid form is equal to in solid form, which is assuring by decreasing the atmospheric pressure .
I am not so sure about this part.
both terms meant different
DeIonized water freezes at 0°C.
Reduced pressure doesn't change that.
No supercooling here, in a dirty beaker with lots of nucleation sites.
Pumping on ice cools it down further, but we don't pump long enough to freeze all the water.
At equilibrium, ice in water T=273.15 K.
We use melting water ice to calibrate thermometers, and in thermocouple cold junctions.