Why does water boil at different temperatures depending on the altitude?

Answer 1

Boiling point is the point at which water undergo a phase change from liquid to gas. A liquid becomes a gas because it has enough kinetic energy to break the intermolecular forces which hold the molecules together as a liquid. One way to increase this kinetic energy is to heat up the molecules by raising the temperature.

The reason that water boils at a lower temperature at a higher altitude is because the pressure exerted upon it from the atmosphere is less at higher altitudes and so it is less "held together". For example, imagine the air as blankets, and the lowest part (sea level) has the most blankets of air stacked on top of one another. This pressure is greatest at the bottom than at the top. Similarly, when you are underwater, and dive deeper you can feel your goggles being pushed more into your head than when you come up, because the water increases more pressure on you the farther down you dive.

So, at a higher altitude, there is lower pressure, which means a smaller force holding the water molecules together. This means that the water requires less energy to overcome the intermolecular forces keeping the water molecules in the liquid phase.

Answer 2

The temperature at which water boils is proportional to the pressure. The higher in altitude you are, the lower the pressure, and the lower the boiling point....

A substance boils when the temperature at which the vapor pressure of the liquid equals the pressure of the surroundings. Thus, if the pressure is 101.3 kPa, the boiling temperature will be 100C, but any change in the pressure will mean a corresponding change in boiling point.

Answer 3

It depends on the air pressure

Boiling in and of itself doesn't really have anything to do with the water being hot...it's just that at different pressures, water boils at a different temperature.

You could put water into a bell jar and vacuum out all of the air (essentially 0 pressure) and the water will boil while cold.

Answer 4

Suppose you were on Mount Everest. There, the atmospheric pressure is lower than it is on the ground. Since during boiling, molecules of water are escaping, it means they have been able to overcome the pressure that was pushing them into the container holding them and thus they have escaped. But if you are at higher altitude, the pressure exerted on the molecules is less.So the molecules require less energy to overcome the pressure and escape. so the water boils at a lower temperature there.

Answer 5

Boiling is very different from evaporation. During evaporation, water molecules at the water surface must gain enough excess energy to break the bonds of surface tension and leave the liquid to float away with the air.

During boiling, enough heat is added at the bottom of the pan to increase the water vapor pressure just enough to form a steam bubble that rises to the surface expanding all the way as it experiences less and less hydraulic pressure. If you take the pan (and heater) to the top of a mountain where the air is thinner and exerts less pressure, less energy must be added to the water to raise its vapor pressure to initiate a steam bubble as it is resisted by the pressure of the liquid above plus the air pressure on top of that. Because less energy is needed, the water can boil at a lower temperature.

In a closed vessel (pressure cooker?) if you raise the water temperature to 212F the pressure inside will be 14.7 psia (or one atmosphere) which will be considerably higher than the air pressure on the mountain. Imagine trying to form a steam bubble at the bottom of the ocean!

Answer 6

Boiling is a phase change. The change is actually an equillibrium process (some particles statistically have enough energy to vaporize, others don't and consequently condense).

As the altitude changes, the ambient pressure decreases because of gravity. Particles tend to sink, so those particles at very high altitude ("edge" of space) doesn't have alot of weight or force on them. Those particles at the bottom of the stack (sea level or below) have the force or weight of all the particles above them pressing down on them.

So, back to equillibrium: what causes a particle to condense? When it loses energy. How does it lose energy? Via collisions. So, what happens to the number of collisions as pressure decreases? It decreases. Hence, at lower pressures, more and more particles have sufficient energy to vaporize (and stay vaporized). The boiling temperature effectively decreases.

Answer 7

Water starts to boil when its vapor pressure reaches its surrounding pressure. At higher elevations the atmospheric pressure is lower and water will boil at a lower temperature. The boiling temperature of water for pressures around 100 kPa can be approximated by

T_v = 100 + 0.0002772 \cdot (p - 101000) - 1.24 \cdot 10^{-9} \cdot (p - 101000)^2

where the temperature is in degrees Celsius and the pressure p is in pascals. One gets the vapor pressure by solving this equation for p.

Answer 8

the effort to boil water takes less energy because of the greater distance between the molecules at the higher altitude...there is less air pressure on the water

Answer 9

Pressure afffects the boiling point of substances.Decrease pressure in high altitudes will lower the boiling point of water.

Answer 10

because it has a higher vapor pressure at higher altitudes