In How can water turn to vapor below the boiling point?, Una said this:
I’d like to add a fifth factor, surface area of the water. Water tends to bead up on skin, reducing its surface area, and by rubbing your hands under the air stream, you keep the surface area maximized.
Sounds sensible to me. There are several other factors I purposefully omitted going into detail on or that were edited out, but increasing the surface area would make a difference at the small scale of rubbing the hands. In thinking about it I wasn’t really considering the water beading so much, as it seems to spread somewhat evenly after soap has removed the oils (referring to my “hard and soft water” Staff report), and I was thinking of a handwashing with soap situation. But your point is still valid even considering that, just at a slightly lower effect. Good point!
My physics teacher at Brooklyn Tech was able to boil water at 0 degrees Celsius, and freeze water at 100 degrees Celsius. All he did was adjust the pressure inside.
remember water freezes/melts at 0 Celsius and boils/condenses at 100 Celsius, both at 1 STP (standard temperature and pressure). He Adjusted the STP in the flask.
Are you sure about that? While it is possible to boil water at a little above 0 C (but not quite at 0 C: Once the pressure gets too low, you sublime straight from a solid to a gas, with no liquid), I don’t think there’s any pressure where water would freeze at 100 C. And if there is, I would be exceedingly surprised if it was achievable in a high school lab demo.
According to this phase diagram, the only solid phase of H[sub]2[/sub]O at 373 K is ice-VII, which occurs at a little over 10,000 atm of pressure. Incidentally, it also bears out what you said: that true boiling transitions (from liquid to vapor) occur only above 0.010 C.
And rubbing your hands together would not only increase the surface area but help break up boundary layers and break up any oily/soapy films on the surface that would otherwise hinder evaporation.
I think of it as the equilibrium:
H[sub]2[/sub]O sub[/sub] <–> H[sub]2[/sub]O sub[/sub]
all the factors mentioned, like removing the H[sub]2[/sub]O sub[/sub] pushes the equilibrium to the right.
Speaking of hard and soft water, salts would also decrease the rate of evaporation.
Thanks for the article, Una.
Also Ice-X and high-pressure Ice-XI, at even higher pressures. Still, I would doubt that you could reach 22000 atmospheres in high school.
It is possible to have water simultaneously freezing and boiling, though, at slightly above zero C and about 0.6% of an atmosphere, which your high school teacher may have shown you. Or boiling without freezing, at slightly higher pressures and nearly that temperature.
Come to think of it, that probably what did happen.