Why does the water under the ice not freeze in the cold season

The density of water at different temperatures is also different, and this is also the principle of thermal expansion and cold contraction.

Generally, when things are hot, the volume expands, and the density decreases accordingly, and when it is cold, the volume decreases, and the density increases.

Water is special, and the density of water is highest at 4 degrees.

So in relatively large bodies of water, such as lakes. In lake water, not all water is the same temperature. When the water is cold, the water at 4 degrees Celsius will sink to the bottom of the lake due to its highest density, and the water at 1 degree or 2 degrees will float on the surface.

When the air temperature is around 0 degrees, the temperature of the lake from top to bottom is like this:

Lake. 0 degrees.

1 degree. 2 degrees.

3 degrees. 4 degrees.

The bottom of the lake. Therefore, when the air temperature is lower than 0 degrees, the water on the lake surface freezes first, and as the temperature gets lower and lower, the ice slowly extends to the bottom of the lake, but the thicker the ice layer, the more it plays the role of blocking the cold air, so the water at the bottom of the lake is generally not frozen.

In addition, the temperature under the ground is higher than that above ground in winter, so in many cases, the temperature of the ground at the bottom of the lake will be greater than 0 degrees, so the water at the bottom of the lake does not freeze.

The first floor is not comprehensive, because the water surface is in contact with the cold air, so it freezes first, and the water below is not easy to freeze because it is in contact with the ground. We all know that the ground is warm in winter.

How do you know not to freeze? The ice on the surface of the water is stretching down little by little, and you can't see it.

The reason why the temperature of water does not change in the process of freezing: ice is a crystal, water in the process of freezing, constantly releasing energy outward, the average kinetic energy of molecules remains unchanged, the distance between molecules becomes larger, the molecular potential energy decreases, and the internal energy of water decreases, so the temperature of water remains unchanged in the process of freezing.

Ice is a crystallization formed by the orderly arrangement of water molecules, which are joined together by hydrogen bonds to form a very "open" (low-density) rigid structure. The spacing between the O—O nuclei closest to the water molecule is that the O—O—O bond angle is about 109 degrees, which is very close to the bond angle of an ideal tetrahedron of 109 degrees 28 minutes.

However, the O-o spacing of each water molecule that is only adjacent and not directly bound is much larger, and the farthest is reached. Each water molecule can combine with 4 other water molecules to form a tetrahedral structure, so the coordination number of the water molecule is 4.

It is due to the lack of condensation nuclei or other conditions in the water, so it remains liquid below 0. Water whose temperature is below zero and does not freeze is called "supercooled water". The reason why water does not freeze after freezing is because if you want liquid water to freeze, you need an ice core——— a crystal becomes an ice core, and the other crystals condense around the ice core.

In fact, the image point is:

Water is made up of water molecules, and when the temperature of the water reaches 0, the water molecules are ready for solidification, that is, freezing, but at this time it is embarrassing, and some water molecules need to freeze first, and "lead" other water molecules to freeze happily together, but at this time, if no one takes the lead in this "leading role".

These water molecules will dry up, and no one will freeze until one of the water molecules freezes first. If the ambient temperature is lower than the temperature of the water, the temperature of the water will continue to decrease, but it will not freeze and become a "supercooled" liquid below 0.

At this time, if you shake the bottle of supercooled water vigorously, or throw a stone in the lake of supercooled water, the water molecules are strongly shaken or squeezed externally, and some water molecules will freeze quickly first, because the temperature of the water is much lower than 0, so the water molecules in the bottle will freeze quickly around them.

Water needs to freeze at a temperature of 0 degrees Celsius or less. In the water there is a frozen nucleus, and with the frozen nucleus, the water molecules that are moving around can be arranged according to the crystal structure of the ice. It is also necessary that the water contains some small particles, which are the attachment of water molecules when they first freeze, and the small particles contained in the water are also called crystal nuclei.

1. The temperature of water freezing needs to be less than or equal to 0 degrees Celsius. In the water there is a frozen nucleus, and with the frozen nucleus, the water molecules that are moving around can be arranged according to the crystal structure of the ice. It is also necessary that the water contains some small particles, which are the attachment of water molecules when they first freeze, and the small particles contained in the water are also called crystal nuclei.

2. Water freezing is actually a crystallization phenomenon, when the water freezes, the movement of water molecules can not break the hydrogen bonds, hydrogen bonds play a major role, it ties up the water molecules to form a regular spatial structure structure, in a crystal lattice, four hydrogen atoms are at the apex of the regular tetrahedron, and an oxygen atom is located in the center of the tetrahedron. In this way, the intermolecular voids become larger and remain constant, so that the volume of water becomes larger when it freezes. The movement of molecules in water can not only destroy the hydrogen bond binding between water molecules but also prevent the molecules from making violent movements lead to frequent collisions between molecules, and the molecules can slide relative to each other and interleave, so that they will fill the gaps with each other, so that the volume becomes larger.

Because water is a poor conductor of heat, water freezing tends to start at the surface. The density is greatest at 4 degrees Celsius. In winter, the water at four degrees Celsius is considered to be muddy water with crushed grains, and they will inevitably "sink" to the bottom of the river, so that the relatively hot water cannot float up and be cooled and heated, so this part of the heat can be preserved, and it is not easy to freeze below.

If you are in a low-temperature freezing environment all year round, it will freeze underwater, and the thickness of the ice sheet depends on the time of the low temperature. In addition, the degree of oxygen content of the water flow also has a certain relationship with the underwater freezing, although the oxygen content in the water depends on the flow of the water source, but the water source itself does not produce oxygen, and the oxygen content mainly comes from the compatibility of oxygen and water, so when the river surface is frozen, there will be a lack of oxygen underwater.

1) Because water below 4 degrees Celsius has the characteristic of abnormal expansion. When the air temperature decreases, the surface of the water freezes at zero degrees Celsius, but the bottom of the water is still above zero, and it does not freeze immediately. The outside air temperature drops again, the thickness of the ice increases, and the temperature below is always higher than the zero stuffy type of water, and the temperature of the bottom water is 4 degrees Celsius.

2) In addition, because ice is a hot poor rent-conducting motif, this layer of ice has a thermal insulation effect on the water underneath, so the water below will not freeze completely immediately.

3) The water under the ice is in direct contact with the soil on the surface of the earth, and the earth constantly emits geothermal heat, so that the water under the ice constantly obtains heat, and also makes it difficult for the water to freeze immediately.

1.Evaporation – During the process of cooling the hot water to the initial temperature of the cold water, the hot water loses some of its water due to evaporation. Less mass makes water easier to cool and freeze.

This way the hot water may freeze earlier than the cold water, but the amount of ice is less. If we assume that water only loses heat through evaporation, theoretical calculations show that evaporation explains the MPEMBA effect. This explanation is plausible and intuitive, and evaporation is indeed an important factor.

However, this is not the only mechanism. Evaporation cannot be explained by experiments done in a closed vessel where no water vapor can leave. Many scientists claim that evaporation alone is not enough to explain the experiments they have done.

2.Dissolved Gases – Hot water retains fewer dissolved gases than cold water, and as it boils, a large amount of gas escapes from the water. Dissolved gases can change the properties of water.

Either make it easier to form convection (and therefore cooler), or reduce the amount of heat required to freeze per unit mass of water, or change the boiling point. There are some experiments that support this explanation, but not theoretical calculations.

3.Convection – Due to cooling, water forms convection currents and uneven temperature distributions. As the temperature rises, the density of the water decreases, so the surface of the water is hotter than the bottom of the water"Hot top"。

If the water loses heat mainly through the surface, then,"Hot top"The water loses heat faster than the temperature is uniform. When the hot water is cooled to the initial temperature of the cold water, it will have a hot top and hence it will cool faster compared to the average temperature but the water with a uniform temperature. Although the thermocap and associated convection can be seen in experiments, it is still unknown whether convection can explain the MPEMBA effect.

4.The things around – the last one of the two glasses of water – have nothing to do with themselves, but with their surroundings. Water with a higher initial temperature may change its surroundings in complex ways, thus affecting the cooling process.

For example, if this glass of water is placed on top of a layer of frost, the frost conducts heat poorly. The hot water may melt this layer of frost and create a better cooling system for itself. Obviously, this explanation is not general, and many experiments do not place the container on the frost layer.

This is the Mpemba phenomenon, the speed of cooling is not determined by the average temperature of the liquid, but by the temperature difference between the surface and the bottom of the liquid, and when the hot water cools sharply, this temperature difference is larger, and it is always greater than the temperature difference of the cold water. The higher the temperature of the upper surface, the more heat is emitted from the upper surface, and therefore the faster the cooling will be. Go for it

Because hot water is more likely to form convection when it encounters cold things, it cools down faster. So warm water freezes faster than cool water in winter.

The effect of warm water freezing faster than cold water is called the Pampaga effect, which has been proven wrong, and it has been proved by three girls in China. At that time, it was Pamper's mother who had not had time to cool the mixture of ice cream ingredients and water and put it in the refrigerator to cool, and as a result, many of the ice cream that had been cooled and put in it did not freeze, but his ice cream did freeze - and indeed it was proved wrong, and the reasons for this result at the time were as follows:

1) He used hot water to dissolve some sugar to make ice cream, and it was too late to cool down, but in this way, because the sugar was not completely dissolved, the freezing point was higher than that of other people's dissolved ice cream, so it was frozen first.

2) He placed the heat-absorbing tubes very close to the refrigerator.

3) The reason why the experiment was like this later was also - mindset.

Therefore, warm water does not freeze faster than cold water.