Chemistry
Temperature
Newtons Laws of Motion

Why does it take longer to boil water at higher altitudes?

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2015-12-25 08:59:53

It doesn't

Actually, at higher elevations, water boils sooner rather than

later.

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

water.

(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).


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