# Why does water vaporize at 70F temperatures
**URL:** https://boards.straightdope.com/t/why-does-water-vaporize-at-70f-temperatures/254918
**Category:** Factual Questions
**Created:** [July 13, 2004, 4:22pm UTC](https://boards.straightdope.com/t/why-does-water-vaporize-at-70f-temperatures/254918 "2004-07-13T16:22:14Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@Wesley\_Clark](https://boards.straightdope.com/u/Wesley_Clark)
#### Post date: [July 13, 2004, 4:22pm UTC](https://boards.straightdope.com/t/why-does-water-vaporize-at-70f-temperatures/254918/1 "2004-07-13T16:22:14Z")
If it rains the water will vaporize pretty quickly. How does this happen exactly since the boiling point of water is 212 F and the temperature outside is usualy 75 or so. So i don’t think the water will boil off, but how does it vaporize away, do small molecules just constantly escape into the air until they are all part of the atmosphere.
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### Author:  [@Nametag](https://boards.straightdope.com/u/Nametag)
#### Post date: [July 13, 2004, 4:27pm UTC](https://boards.straightdope.com/t/why-does-water-vaporize-at-70f-temperatures/254918/2 "2004-07-13T16:27:21Z")
Yes. That is exactly what happens.
Some water will always evaporate unless it’s either freezing or so humid that the air is saturated.
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### Author:  [@Caldazar](https://boards.straightdope.com/u/Caldazar)
#### Post date: [July 13, 2004, 4:43pm UTC](https://boards.straightdope.com/t/why-does-water-vaporize-at-70f-temperatures/254918/3 "2004-07-13T16:43:36Z")
Basically what Nametag said, although ice does vaporize as well; it just does so more slowly than liquid water.
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### Author:  [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)
#### Post date: [July 13, 2004, 4:51pm UTC](https://boards.straightdope.com/t/why-does-water-vaporize-at-70f-temperatures/254918/4 "2004-07-13T16:51:36Z")
The temperature is a measure of the average kinetic energy of the water molecules. However, there is a tremendous range of molecular kinetic energies, and hence velocities, clustered around this average, both above it and below it. And so there are always some molecules that have sufficient energy to overcome the boundry energy and escape into the air.
Likewise there are some water molecules in the vapor in the air that manage to get past the barrier and enter the water. When the air is dry there are many that escape the water and few that return from the air. As the number of molecules in the air increases, more and more go back into the water and eventually the number going out equals the number going in and the air is then said to be “saturated.”
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### Author:  [@minor7flat5](https://boards.straightdope.com/u/minor7flat5)
#### Post date: [July 13, 2004, 4:53pm UTC](https://boards.straightdope.com/t/why-does-water-vaporize-at-70f-temperatures/254918/5 "2004-07-13T16:53:48Z")
At the surface of the water, the molecules are all going at different directions and different speeds. Some of them are going up, but lack the energy to leave the puddle; others have plenty of energy, but are heading slantwise or downwards.
A small few have sufficient energy and are heading upwards – these escape. Since only the most energetic ones escape, the average temperature of the puddle decreases. This is why evaporation cools.
Of course, as the air gets saturated, you have a similar flow of less energetic molecules from the air being caught by the puddle; hence, you can achieve an equilibrium where no evaporation takes place.
Damn. David beat me to it. I’ll let it stand anyway.
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### Author:  [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)
#### Post date: [July 13, 2004, 5:41pm UTC](https://boards.straightdope.com/t/why-does-water-vaporize-at-70f-temperatures/254918/6 "2004-07-13T17:41:28Z")
Una responds:
[http://www.straightdope.com/mailbag/mevaporation.html](http://www.straightdope.com/mailbag/mevaporation.html)
Discussion:
> **[Nitpick re: water vapor - surface area](https://boards.straightdope.com/sdmb/showthread.php?t=257319)**
>
> 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...
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### Author:  [@spingears](https://boards.straightdope.com/u/spingears)
#### Post date: [July 14, 2004, 12:24am UTC](https://boards.straightdope.com/t/why-does-water-vaporize-at-70f-temperatures/254918/7 "2004-07-14T00:24:54Z")
> [@Caldazar](#):
>
> Basically what Nametag said, although ice does vaporize as well; it just does so more slowly than liquid water.
More correctly, water evaporates, Ice sublimates. The rates are highly dependent on both temperature and relative humidity of atmosphere.