The light of science and technology water at room temperature freezes after boiling in a vacuum, why

First of all, you should also clarify what boiling is, although you already have a deeper understanding.

The process of intense vaporization of a liquid (water), but it depends on two conditions, one is temperature and the other is pressure. But further, this pressure is not actually atmospheric pressure, but refers to the pressure generated by the water vapor in the atmosphere above the liquid water. In fact, we all know that there is water vapor in the air, but when the temperature decreases, a part of the water vapor will liquefie, and the pressure of the water vapor at this temperature corresponds to the water vapor at that temperature"Saturation pressure".

In the case of water, for example, at 100 degrees Celsius, the saturation pressure of the water is one atmosphere, so the water in an open container boils as soon as it is boiled, but if it is in a pressure cooker, the boiling temperature rises. This process is an intermolecular equilibrium process and has nothing to do with the exact temperature. (Even when a liquid becomes solid, the simple example is that ice sublimates).

Further, because the spacing between gas molecules (or atoms) is much greater than that between liquids, the intermolecular potential energy increases, therefore, due to the balance of energy, the liquid will inevitably absorb a certain amount of energy when it is vaporized. That is, the heat of vaporization (this"gas"The word seems to be"Steam", I can't remember exactly).This energy is larger.

From the above, we conclude that the process you are talking about should actually be the process of water vaporization and then heat absorption, rather than the energy you imagine first and then vaporize the water (although this is often the case in daily life).This is actually a habitual wrong thinking, and everyone is prone to make it.

I would like to add that in fact, the comrade in front of me is correct, but it is simpler.

The vacuum in the vacuum hood (vacuum chamber) you are talking about is obtained by vacuum acquisition equipment such as vacuum pumps. Because you take out the air in the vacuum chamber when you vacuum, the pressure inside becomes smaller, and the water molecule gets more chance to move freely, and it (the water molecule) evaporates into the vacuum hood, and we know that any substance needs energy to change from a liquid state to a gaseous state, and water molecules are no exception. And so it loops:

Water absorbs heat and becomes gaseous; Then the water vapor is pumped away by a vacuum pump, and then the air pressure becomes lower and the water evaporates again, and the cycle repeats itself to absorb a large amount of heat. In this way, the heat in the water is taken away by the evaporated water molecules, and the remaining water turns into ice because the temperature becomes very low.

If there is very little water, it will be completely pumped away, and as long as there is water in it, its vacuum level will be more than 260pa.

Because the water molecules evaporate, they take away a lot of heat. It is important to note that water undergoes a change of state of matter, that is, when it changes from water to water vapor, it needs to absorb more heat than its own specific heat; In turn, it loses more heat, and this loss of heat is enough to reduce it below 0 under normal conditions, so it freezes.

I think the above two are right, and the outside heat that is a vacuum inside will not be easily transferred in.

Yes, water boils first in a vacuum because the air pressure is lower than the saturated vapor pressure of the water temperature at that time, and the continuous boiling will reduce the temperature of the water to its freezing point and finally freeze into ice.

Water in a liquid state needs to have a certain pressure range as well as a certain temperature range. If the liquid water is at a fixed temperature and constantly reduces the pressure of the surrounding environment, the water will boil immediately. Similarly, if liquid water is at a constant pressure and constantly lowers the ambient temperature, it will cause the water to freeze immediately!

Both temperature and pressure change the phase of water

When the pressure in the environment around liquid water decreases, the boiling point of the water decreases. We are very familiar with this phenomenon, at high altitudes, water boils at lower temperatures; This is because the atmosphere at high altitudes is thinner, the pressure on the surface of the water decreases, and the water molecules will escape when they gain less kinetic energy.

If we increase the pressure on the surface of the water, the water molecules need more kinetic energy, which is the temperature, to jump out of the water. If the liquid water is constantly lowering the ambient temperature at a fixed pressure, it will cause the water to freeze immediately!

1. Reason: Due to the decrease of the vapor pressure of the leakage of water, a large amount of water volatilizes and takes away the heat, resulting in freezing;

2. The freezing point of water will increase with the decrease of pressure;

3. When the water temperature drops to 0 degrees Celsius, the water freezes, and when the water freezes, almost all the molecules are associated together to become a huge association molecule;

4. In ice, the arrangement of water molecules is that each oxygen atom has four hydrogen atoms as neighbors, and two hydrogen bonds are close neighbors, and this arrangement leads to an open structure;

5. There are large voids in the structure of ice, so the density of ice is smaller than that of water at the same temperature;

6. Water coexists in gaseous and liquid states at the temperature of Changhuiqing;

7. The temperature coexists in the gaseous state and the solid state below zero degrees Celsius;

8. Coexist in gaseous liquid state at zero degrees Celsius;

9. If water exists in a vacuum outside the Earth's atmosphere, it exists mainly in a gaseous state.

When the air pressure decreases, the boiling point of the water will also decrease, and the water will start boiling; The water turns into water vapor, which reduces the internal energy of the water and freezes the water.

Barometric pressure is the atmospheric pressure acting on a unit area, i.e., the gravitational force exerted on a vertical column of air that extends up to the upper boundary of the atmosphere per unit area. The famous Magdeburg hemispheric experiment proves its existence. The SI unit of air pressure is Pascal, abbreviated Pa, and the symbol is Pa [1].

In meteorology, people generally use kilopascals (kpa) or hectopa (hpa) as the unit. Other commonly used units are: bar (1 bar = 100,000 Pa) and centimeters of mercury (or centimeters of mercury).

Air pressure varies not only with altitude but also with temperature. Changes in air pressure are closely related to weather changes.

Abbreviation for atmospheric pressure. is the atmospheric pressure acting on a unit area, i.e., equal to the weight of the vertical column of air per unit area that extends upwards to the upper boundary of the atmosphere. The magnitude of the air pressure is related to conditions such as altitude, temperature, etc.

Generally, it decreases with increasing height. In the horizontal direction, the difference in atmospheric pressure causes the flow of air. A unit of air pressure, and it is customary to use the height of the mercury column.

For example, a standard atmospheric pressure is equal to the weight of a 760 millimeter-high column of mercury, which is equivalent to the atmospheric pressure of a kilogram on an area of one square centimeter. It is used in an international uniform manner"hPa"As a unit of air pressure. After conversion:

One standard atmosphere = 1013 hPa (millibar). The average annual air pressure in Shenzhen is 10 pascals.

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 extremely short, and the effect is not continuous, but a large number of molecules frequently collide with the vessel wall, and the force on the vessel wall is continuous and uniform, and the ratio of this pressure to the area of the vessel wall is the pressure strength is small.

Because there is no atmospheric pressure in a vacuum, the boiling point of water drops below room temperature, causing the water to boil and become water vapor.

And we all know that liquids absorb a lot of heat when they vaporize. This will make it cooler in that environment. When the temperature is lower than its condensation point! Water vapor condenses directly into ice (frost).

When the air pressure of water decreases in a vacuum, the boiling point of the water will also decrease, and the water will start to boil; The change of water into water vapor reduces the internal energy of the water, and the water freezes.

In a vacuum, the boiling point of water becomes lower, and a large amount of water vapor absorbs heat and freezes.

Because in a vacuum, the boiling point of water will be lower than room temperature.

Water has a low boiling point in a vacuum, so it boils first.

Because water can lower the boiling point in a vacuum.

Because in a vacuum, the boiling point of water is comparatively lower.

Because the boiling point of water in a vacuum is relatively low, it will boil first.

The boiling point of liquids on Earth is related to the pressure in the atmosphere! When the atmospheric pressure is less, the boiling point decreases!

It may be that the pressure in the vacuum is different, so the formation process is different.

If the process of converting into gaseous water is too violent, the water will boil first, and the vaporization process will absorb a lot of heat, so that the temperature in the container will drop rapidly, and when it drops below 0, the liquid water freezes.

The water boils first, and the vaporization process absorbs a lot of heat.

Because the boiling point of water in a vacuum is relatively low, it may be lower than the temperature of the surrounding environment.

Because the air pressure drops, it boils, and then the heat dissipates and freezes.

Because there is no medium in the vacuum, the heat dissipation is particularly fast.

This is because the boiling point of water is very low in a vacuum.

As a result, the evaporation rate of water is accelerated, and part of the liquid water is converted into gaseous water, and if the process of conversion into gaseous water is too violent, the water will boil first.

Because the water molecules evaporate, they take away a lot of heat. It is important to note that water undergoes a change of state of matter, that is, when it changes from water to water vapor, it needs to absorb more heat than its own specific heat; In turn, it loses more heat, and this loss of heat is enough to reduce it below 0 under normal conditions, so it freezes.