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Ask Dr WLS Your Own Question

Dr WLS
Dr WLS, PhD
Category: General
Satisfied Customers: 483
Experience:  PhD degree in engineering/physics , online tutor since 1994 in general subjects
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Why does water boil slower at higher altitude

Customer Question

why does it take water longer to boil at 5000 feet than it doe at sea level
Submitted: 10 years ago.
Category: General
Expert:  Dr WLS replied 10 years ago.

It actually takes less time to boil water at higher elevations, at a given heat setting of the stove, because the water starts boiling begins at a lower temperature, and remains at that temperature while it boils. What I think you meant to ask is "Why does cooking food by boiling take longer at 5000 feet than it does at sea level?"


The reason this is true is twofold: (1) Water starts boiling when the temperature is high enough to make the vapor pressure equal to the atmospheric pressure. Vapor pressure, which measures the tendency of water molecules to escape the surface, rises with liquid temperature. When the outside pressure is reduced, a lower vapor pressure and therefore a lower temperature is sufficient to allow boiling. (2) The atmospheric pressure gets lower as altitude increases, because of the reduced amount of atmosphere above.

Customer: replied 10 years ago.
Reply to Dr WLS's Post: Dr
Thank you for your prompt response.
I am starting to thing that my hypothesis is incorrect.
According to your answer food should cook faster by boiling when you are at 5000ft that when you are at see level.
Is this a correct deduction?

Charles Hammonds DPM
Expert:  Dr WLS replied 10 years ago.

<<According to your answer food should cook faster by boiling when you are at 5000ft that when you are at see level.
Is this a correct deduction? >>


No, that is not what I meant to say. The water comes to a boil sooner at higher altitudes (like 5000 ft), but it boils at a lower temperature. There is a slower rate of heat transfer to the food at the lower temperature, and cooking occurs more slowly.


If you go to a high enough altitude and low enough atmospheric pressure, water can even boil at room temperature, but you won't be able to cook anything that way.


Customer: replied 10 years ago.
why does it take water longer to boil at 5000 feet than it doe at sea level


Sent September 04 2006 at 10:27am (9 hours and 39 minutes later)
Dr
Thank you for your prompt response.
I am starting to thing that my hypothesis is incorrect.
According to your answer food should cook faster by boiling when you are at 5000ft that when you are at see level.
Is this a correct deduction?

Charles Hammonds DPM
Expert:  Dr WLS replied 10 years ago.
Please read my answer above to the same question, which you have posted twice, six minutes apart.