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Why water doesn't boil beyond 100 degrees?

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Pure water boils at 100 C only when the ambient pressure is 1 atm. If you were to take your pot of water up to the top of a tall mountain and start to boil it, your pot of water would boil at a temperature significantly less than 100 C, because the ambient pressure is no longer 1 atm. For example, at an elevation of 3000 m above sea level, the boiling point of water is reduced to about 90 C. Conversely, if one heats water in a closed environment where the pressure is greater than one atmosphere, boiling will not occur until the temperature exceeds 100 C. The boiling point of water can be changed also by dissolving another substance in it or mixing it with another substance. That is the principle behind adding anti-freeze to the water in a car radiator: not only is the boiling point of the mixture raised above 100 C, but the freezing point of the mixture is reduced below 0 C. On a hot day, the water in the radiator stays liquid above 100 C because the cooling system also is pressurized to a certain extent. If the radiator cap is removed suddenly, the pressure inside the cooling system drops at once to ambient, and the hot coolant can begin to vaporize.

Reference https://www.physicsforums.com/threads/why-doesnt-boiling-water-exceed-100-deg-c.766189/
Best Answer: It depends on the air pressure.
I am assuming you are talking about pure water because impurities can make it boil at a higher temperature.
In an airplane when the pressure is lower water boils at a lower temperature.
In a pressure cooker when the pressure is higher water boils at a higher temperature.
It is because the air pressure stops the molecules of water jumping out of the water.
At a higher pressure the molecules have to be more exited to get out as steam.
At a lower pressure they can get out easier because the air pressure is not pushing them in with quite so much force.

This is a important question . it has been asked many of times in jee main . Pure water boils at 100 C only when the ambient pressure is 1 atm. If you were to take your pot of water up to the top of a tall mountain and start to boil it, your pot of water would boil at a temperature significantly less than 100 C, because the ambient pressure is no longer 1 atm. For example, at an elevation of 3000 m above sea level, the boiling point of water is reduced to about 90 C. http://www.engineeringtoolbox.com/boiling-points-water-altitude-d_1344.html Conversely, if one heats water in a closed environment where the pressure is greater than one atmosphere, boiling will not occur until the temperature exceeds 100 C. The boiling point of water can be changed also by dissolving another substance in it or mixing it with another substance. That is the principle behind adding anti-freeze to the water in a car radiator: not only is the boiling point of the mixture raised above 100 C, but the freezing point of the mixture is reduced below 0 C. On a hot day, the water in the radiator stays liquid above 100 C because the cooling system also is pressurized to a certain extent. If the radiator cap is removed suddenly, the pressure inside the cooling system drops at once to ambient, and the hot coolant can begin to vaporize. This page explains a little more behind the physics of the boiling point: http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/vappre.html

Reference https://www.physicsforums.com/threads/why-doesnt-boiling-water-exceed-100-deg-c.766189/