Re: What is the boiling point of water on top of Mount Everist

There are really two aspects to answering this question.

The first is that the atmospheric pressure decreases with altitude.  At 
higher altitudes, the "weight" of air above you is less, so the pressure 
is lower (just like the pressure is higher at the bottom of the ocean).  
This is discussed here: 
 http://w
ww.pbs.org/wgbh/nova/everest/exposure/pressure.html

At the top of Mount Everest, the atmospheric pressure is about one-third 
of what it is at sea level, as discussed on these two pages
 http://www
.pbs.org/wgbh/nova/everest/exposure/higher.html http://www.mos.org
/Everest/exhibit/physiology.htm
These also discuss some of the physiological effects of the decrease in 
pressure.

The second aspect is the effect of atmospheric pressure on the boiling 
temperature.  Boiling happens when the vapor pressure exerted by the water 
equals the atmospheric pressure.  So boiling is easier (can happen at 
lower temperatures) when the pressure is lower, as explained here:
 http://www.iapws.org/faq1/boil.ht
m

So yes, altitude matters for boiling.  At sea level, water boils at 
approximately 100 degrees Celsius.  In the Denver area where I live, the 
atmospheric pressure is about 83% of that at sea level, and water boils at 
about 95 degrees C.  Atop Mount Everest, it is about 34% of sea level, 
which translates into boiling at about 72 degrees C.

Allan Harvey, aharvey@boulder.nist.gov
"Don't blame the government for what I say, or vice-versa."