Problem description:
The boiling point of water at high altitude will be lower than normal ~ then there is enough altitude in theory ~ is it possible for water to boil below zero degrees Celsius?
Analysis:
This question is actually very difficult!
Consider the boiling point first.
Have you noticed that when boiling water in a pot, heat it for a while, and then
You will see many small bubbles near the bottom of the pot. With the increase of temperature,
The bubble is getting bigger and bigger. This is because the bottom of the pot is heated quickly, close to the water head at the bottom of the pot.
First, it turns into steam, forming bubbles in water; At the same time, it was originally soluble in water
In the air, small bubbles will be formed due to heat precipitation and expansion, and the surrounding area will be
Hot water will evaporate water vapor into small bubbles, which will gradually become larger. while
When heated to a certain temperature, these bubbles in water become quite large because
Buoyancy will rise, and it will break when it reaches the surface. This liquid
The simultaneous rapid gasification of the interior and the surface is called boiling.
At this moment, we say that the water is boiling. The temperature at which water boils is called the boiling point of water.
We usually say "the boiling point of water is 100℃", which means at one atmospheric pressure.
(101.5kpa) The boiling temperature of water. So is the boiling point of water 10%?
What about the same? That's not true. The boiling point of water changes with the change of atmospheric pressure.
With the increase of air pressure, the boiling point rises. Because of the atmospheric pressure on the water, there will always be
It is to prevent water molecules from evaporating, so the air pressure rises and the water melts.
Water vapor must have a higher temperature. Generally on the ground at low altitude,
Atmospheric pressure is basically one atmosphere. Below sea level, eg very low.
Deep mine), the air pressure is higher than one atmosphere, where water is boiled, and the water boils.
This should be mentioned. It is measured that the boiling point of water will rise by 3 degrees for every kilometer of depth increase.
On the contrary, if the air pressure decreases, the boiling point will also decrease. For example, the higher the altitude, the more empty it is.
The thinner the gas, the lower the air pressure, and the boiling point of water in this place decreases. exist
Boil water on Mount Everest, the top of the world. As long as it reaches 73.5℃, water will
It is burning. Such "boiling water" can't cook food, and it can't be cooked.
Kill some bacteria. Therefore, geologists and mountaineers work on high mountains.
When cooking, everyone should use a pressure cooker-a pressure cooker. It boils at high pressure.
Made by the principle of point elevation. The sealed pot cover prevents the steam in the pot from escaping,
So the air pressure increases, the boiling point rises, and the food is cooked quickly.
Next is the freezing point, because we are talking about water (liquid) instead of ice (solid).
Thermodynamic freezing point is based on the temperature when solid and liquid coexist in water.
Yes, it's 0℃ at standard atmospheric pressure.
If it is pure water alone, the pressure will cause the freezing point to drop. (But
Cause the boiling point to rise! ! In addition, adding water-soluble substances, such as salt, also
Is one of the methods, because when any substance is dissolved in water, it will lower the freezing point of water.
(0℃)。 As for how much the temperature can be reduced, it needs to be explained by experiments.
In reality, the existence of condensation nuclei is an important factor.
Asked an elder, he said: if it is pure water, there is no impurity at all, normal atmospheric pressure.
Even if the water temperature drops to MINUS 40 degrees, water can remain liquid without freezing, which is "supercooled water". He asked again: If this "supercooled" water is suddenly disturbed, will it freeze instantly? The elder replied: No (! ! )
Attached drawings: (img172.photo.163/ivy 7070/* * * * * * * * * * * * *. gif)
This diagram is the so-called three-phase diagram of ice or water (i.e. solid, liquid and gas).
The temperature at which ice, water and steam coexist at the same time is the triple point.
Is 0. 1 degree Celsius, the minimum temperature of water will decrease with the increase of pressure, but
Please pay attention to the unit and value of pressure in the figure, which is not the general reality.
Check what can be achieved!
(others: the basis of classical thermodynamics,
Gordon j van wylen, Richard e Sonntag, page 40) has a picture of water. It can be seen that with the increase of pressure, the solidification temperature will decrease. Only the first phase of ice, other phases of ice, the solidification temperature will increase with the increase of pressure, so the lowest temperature of water should be the triple point where ice and water coexist in the first and third phases.
Therefore, if someone is willing to use calculus to deal with the above figure and find the extreme value (for example, at 0℃, if there is a triple point-boiling point, is its air pressure negative), it should be able to get an accurate explanation. Now I can only say: If the "other" data is correct, and considering the exponential factor of the solution in impure water, it can be basically determined that water at zero degree is likely to boil.