# Nitpick re: water vapor - surface area
**URL:** https://boards.straightdope.com/t/nitpick-re-water-vapor-surface-area/246254
**Category:** Cecil's Columns/Staff Reports
**Created:** [May 20, 2004, 10:35pm UTC](https://boards.straightdope.com/t/nitpick-re-water-vapor-surface-area/246254 "2004-05-20T22:35:43Z")
**Posts on this page:** 8
**Page:** 1
### Author:  [@CurtC](https://boards.straightdope.com/u/CurtC)
#### Post date: [May 20, 2004, 10:35pm UTC](https://boards.straightdope.com/t/nitpick-re-water-vapor-surface-area/246254/1 "2004-05-20T22:35:43Z")
In [How can water turn to vapor below the boiling point?](http://www.straightdope.com/mailbag/mevaporation.html), Una said this:
> [@](#):
>
> Now let’s focus on your example. The rate of evaporation from your skin is determined by four primary factors:
>
> 1. The temperature of your skin.
> 2. The temperature of the ambient (surrounding) air.
> 3. The amount of water in the air relative to the amount it can hold (the relative humidity).
> 4. The ambient air pressure.
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.
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### Author:  [@Una\_Persson](https://boards.straightdope.com/u/Una_Persson)
#### Post date: [May 20, 2004, 11:11pm UTC](https://boards.straightdope.com/t/nitpick-re-water-vapor-surface-area/246254/2 "2004-05-20T23:11:07Z")
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!
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### Author:  [@capacitor](https://boards.straightdope.com/u/capacitor)
#### Post date: [May 22, 2004, 6:05pm UTC](https://boards.straightdope.com/t/nitpick-re-water-vapor-surface-area/246254/3 "2004-05-22T18:05:37Z")
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.
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### Author:  [@Chronos](https://boards.straightdope.com/u/Chronos)
#### Post date: [May 23, 2004, 7:19pm UTC](https://boards.straightdope.com/t/nitpick-re-water-vapor-surface-area/246254/4 "2004-05-23T19:19:04Z")
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.
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### Author:  [@Mathochist](https://boards.straightdope.com/u/Mathochist)
#### Post date: [May 23, 2004, 7:43pm UTC](https://boards.straightdope.com/t/nitpick-re-water-vapor-surface-area/246254/5 "2004-05-23T19:43:44Z")
> [@Chronos](#):
>
> 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](http://www.lsbu.ac.uk/water/phase.html), 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.
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### Author:  [@antechinus](https://boards.straightdope.com/u/antechinus)
#### Post date: [May 24, 2004, 5:53am UTC](https://boards.straightdope.com/t/nitpick-re-water-vapor-surface-area/246254/6 "2004-05-24T05:53:56Z")
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.
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### Author:  [@Chronos](https://boards.straightdope.com/u/Chronos)
#### Post date: [May 24, 2004, 10:51pm UTC](https://boards.straightdope.com/t/nitpick-re-water-vapor-surface-area/246254/7 "2004-05-24T22:51:29Z")
> [@](#):
>
> According to this phase diagram, the only solid phase of H2O at 373 K is ice-VII, which occurs at a little over 10,000 atm of pressure.
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.
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### Author:  [@capacitor](https://boards.straightdope.com/u/capacitor)
#### Post date: [May 25, 2004, 12:14am UTC](https://boards.straightdope.com/t/nitpick-re-water-vapor-surface-area/246254/8 "2004-05-25T00:14:15Z")
Come to think of it, that probably what did happen.