Why is the lower the pressure, the lower the boiling point

Air pressure and boiling point.

The boiling point of a liquid generally varies with the pressure of the surrounding atmosphere, and when the air pressure is low, the boiling point of water decreases. On a plateau of more than 6000 meters, the air pressure is lower, and the water reaches 80

As soon as it was boiled, the water began to vaporize in full force, the temperature no longer rose, and the rice was not cooked. In the pressure cooker, due to the high air pressure, the valence and electrons must have a high rate to reach boiling, so the temperature in the pot is also high, more than 100, so that the cooking with the pressure cooker is cooked quickly.

Because in the molecules of gases, valence and electrons are in three-dimensional operation, the shell formed by operation makes the molecules repulsive, when the pressure is high, the distance between the molecules is forced to be closer, and the repulsion force generated by valence and electrons interferes with each other, and the core increases the rate of valence and electrons to increase the repulsion, and the frequency of repulsion (the number of times each part appears per second) The valence and the rate of electrons are high, and the temperature of the substance increases. Conversely, the pressure decreases, the distance between the molecules increases, and the valence and electron rates are correspondingly lower.

When water is under greater pressure, valence and electrons must have a higher rate to produce enough repulsion to form vaporization. And for the valence and electrons to have a higher rate, it must have a higher temperature, so when the pressure is high, the boiling point of water is high.

When the plateau air pressure is low, the valence of water and the rate of electrons do not need to be very high, and there is enough repulsion to push the distance between the molecules, and the conditions for vaporization to occur are reached. That is, when the water temperature is not very high, internal vaporization has taken place, so the boiling point is low.

Because pressure is kinetic energy and heat is potential energy. If the pressure decreases, it means that the distance of the electron from the surface of the nucleus increases, resulting in the simultaneous decrease of the two forces at the equilibrium position of the electron, that is, the force of the boiling point decreases at the same time, so the lower the pressure, the lower the boiling point.

The lower the air pressure, the lower the boiling point, and the boiling point of water changes with the change of atmospheric pressure: the boiling point increases as the air pressure increases. Because the atmospheric pressure on the surface of the water always prevents water molecules from evaporating, when the air pressure rises, the water must have a higher temperature to turn into water vapor.

Conversely, when the air pressure decreases, the boiling point decreases. For example, the higher the altitude, the thinner the air and the lower the air pressure, the boiling point of water in this place decreases.

Barometric pressure is the atmospheric pressure acting on a unit area, i.e., equal to the weight of a column of vertical air per unit area that extends upwards to the upper boundary of the atmosphere. The famous Magdeburg Hemisphere Sail Test proves its existence. The international unit of air pressure is Pascal, abbreviated as Pa, and the symbol is Pa.

According to the theory of molecular dynamics, the pressure of a gas is caused by a large number of molecules frequently colliding with the walls of the container. The collision time of a single molecule on the container wall is very short, and the effect is not continuous, but a large number of molecules frequently collide with the empty vertical wall like hailstone, and the force on the wall is continuous and uniform, and the ratio of this pressure to the area of the wall is the pressure strength is small.

Boiling is a phenomenon of violent vaporization that occurs simultaneously inside and on the surface of a liquid at a certain temperature. The boiling point is the temperature at which the liquid boils, that is, the temperature at which the saturated vapor pressure of the liquid is equal to the external pressure. The higher the concentration of the liquid, the higher the boiling point.

The boiling point of different liquids is different. The boiling point changes with the change of external pressure, and the low pressure is also the low boiling point.

Categories: Education Town, Science, >Travel, Infiltration, Science and TechnologyProblem Description:

The higher the pressure, the higher the boiling point I know But I want to ask if the boiling point of water is 100 degrees Celsius, put it in a pressure cooker and boil it, and the boiling point increases to 120 degrees Celsius (let's say), then the boiling point increases, doesn't it take longer to reach 120 degrees? So why is it that the higher the boiling point, the faster things cook?

Analysis: This is because of the vapor pressure of the water.

At atmospheric pressure, water is saturated with steam at 100 degrees, but in the presence of pressure, water needs a higher temperature to saturate the water vapour. Think about it, in a stressful situation, the molecular attraction of water molecules to break away from the surface of the water also requires a higher energy to escape, and this energy is to raise the temperature of the water.

When cooking food, it has nothing to do with boiling water, temperature is the key.

The temperature at which water boils is called the boiling point of water, and we usually say that "the boiling point of water is 100", which refers to the temperature at which water boils at one atmosphere (standard atmospheric pressure). So is the boiling point of water set in stone? No.

The boiling point of water varies with the change of the trillionage of atmospheric pressure: as the air pressure increases, the boiling point increases. Because the atmospheric pressure on the surface of the water always prevents water molecules from evaporating, when the air pressure rises, the water must have a higher temperature to turn into water vapor.

Generally at low altitudes, atmospheric pressure is basically one atmosphere. Boiling water at a place below sea level (e.g., in a very deep mine hood) where the air pressure is one atmosphere higher and the boiling point of the water rises, and it has been determined that an increase in depth of one kilometer increases the boiling point of the water by 3 degrees.

On the contrary, when the air pressure decreases, the boiling point decreases. For example, the higher the altitude, the thinner the air and the lower the air pressure, the boiling point of water in this place decreases. Boil water on Mount Everest, the top of the world, and as soon as it is boiled, the water is boiled "boiled".

Such "boiling water" does not cook the meal and does not kill certain bacteria. For this reason, geologists and mountaineers use high-pressure cookers – pressure cookers – when working in the mountains. It is made using the principle of rising boiling point under high pressure.

The sealed lid prevents the vapor inside the pot from escaping, so the air pressure increases, the boiling point increases, and the meal cooks quickly. Under normal use, the air pressure in the household pressure cooker is an atmospheric pressure, and the temperature is generally around 125. When the air pressure in the pot is too high, the safety valve on the pot will automatically open to release a part of the vapor and reduce the air pressure.