Why does it take longer to boil water at higher altitudes?
Actually, at higher elevations, water boils sooner rather than
At higher altitudes, air pressure is lower. The reduced air
pressure lowers the temperature at which water boils in an open
container. So, water actually boils faster at higher altitudes, but
it takes longer to cook foods because the water boils at a lower
temperature. This lower temperature slows down the physical and
chemical changes that take place when foods are cooked in
(Sometimes it can take water longer to boil at higher altitudes
simply because it is often colder and windier at high altitudes (if
you camping), and so it will take longer to heat the water).
If you are taking a chemistry class right now, you might recall
your teacher talking about Gay-Lussac's law of P1/T1 = P2/T2.
Therefore, given that the volume is constant, as the pressure
changes from 1 ATM to a lower number, say .5, temperature must also
change in proportion to the atmosphere to fit the equation. The
temperature would decrease by 1/2.
See the Related Questions link to the left for more
information about how barometric pressure and elevation effect the
boiling point of water.
Following the idea of higher altitudes/lower atmospheric
pressure, there will be less initial dissolved oxygen in the higher
altitude water compared to a pot of water in lower altitudes. This
will decrease the quantity of bubbles (oxygen escaping from the
water) you see as the water heats but before the water actually
begins to boil. If you confuse these bubbles with boiling it will
seem as though you are not reaching a boil as quickly as when there
is more dissolved oxygen and more bubbles.
The following correction is from a science major with chemistry
minor: the above is almost true, but Gay-Lussac's law is expressed
a different way. It is P1/T2=P2/T1. What the above formula
describes is Boyle's law (P1/T1=P2/T2).