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Does atmospheric pressure act as resistance against water that prevents it from boiling? Water boils at lower temperatures at lower pressures. Does this mean that water would naturally prefer to exist as a gas?

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  • $\begingroup$ Your second question is not well defined. I could ask the question 'do gentlemen naturally prefer blondes?' and it would be as clear. What do you mean by 'naturally', and what thermodynamic conditions are provided? $\endgroup$ – Jon Custer Jan 22 '15 at 23:55
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Yes it does. As water gets hotter, from 0 C and up, it has an increasing "vapor pressure." This is the push of water into steam from the water. The reason water on the stove boils at about 100 C is because at 100 C, the vapor pressure of water is equal to the air pressure! So below that temperature, the air pressure is able to keep the water from boiling. Above that temperature, the steam from the water has higher pressure than the air, and it comes bubbling out of the water into the air.

If you go to high altitude say 4000 m, air pressure is only about 60% what it is at sea level. At that altitude, water will boil at 87 C, 13 degrees cooler than at sea level! This is because with less air pressure holding the steam in the water, the water doesn't have to get as hot to over come the air pressure with its vapor pressure.

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