Why does the water freeze from the edge to the middle?

Icing is a multifactorial phenomenon, and the factors are simply listed: heat conduction.

It must be from the outside to the inside, the weather is cold for a pool.

The water of this system is coming from the outside in, and obviously should first freeze on the outside, due to the surface energy.

All changes start from the interface (including the gas-liquid and solid-liquid interface), which obviously also supports the freezing of the outside first, and the relatively high nearshore domestic sewage, resulting in the reduction of the freezing point, which is a negative effect to a certain extent, and should freeze first in the middle; When the edges and surfaces are already frozen, the inside is less likely to freeze, because the icing needs to expand, and there is solid ice all around, and it is obviously more difficult for the internal water to expand into ice, which obviously supports the outer edge to freeze thicker. In addition, the cooling power of the intermediate water is mainly on the vertical surface, and the cooling power of the edge water is both on the upper surface and on the side surface. The specific heat capacity mentioned above.

It is also a reason that the specific heat capacity of the substance in contact with the surface is smaller, while the specific heat capacity of water is larger, so it is becoming more and more difficult to freeze from the outside in. <>

Ask if it is first, and then why. Does the water freeze from the edge to the middle? Not necessarily, but most of the time it is.

Let's start with a law that may not be very accurate: almost all changes in nature begin at the most uneven and stable place. This is especially true for crystallization problems such as water freezing.

Where is the most unstable place in water? One is the border, surface and bottom of the water that is in contact with non-water, and the other is where there are impurities in the water. ("Phase" can be simply understood as other substances, and this "substance" here distinguishes water and ice into two substances.)

The "impurities" here include substances that are soluble in water, because they make the solution of this concentration of 0 non-zero and non-homogeneous, there is a concentration gradient) Therefore, water freezing must have started from these places. Therefore, most of the ice on the surface of the water starts from the edge, and a few times it starts from some impurities in the middle. If the ice has already begun, it can be understood that the process described above returns to the initial conditions of the imminent freezing, so it is better to start from the edge of the ice that has already been frozen or where there are impurities (here "impurities" include the ice that has already frozen), and repeat it continuously, and you will see that the water will freeze from the edge to the center, and because it starts from these places, it will gradually accumulate, and the new ice will be wrapped around the old ice, so that the edge will be thick around the edge and thin in the middle.

If the temperature is cooled from above zero to just zero degrees, the water will not freeze, because when the freely moving water molecules are attracted to each other and arranged in a neat lattice, the energy of the water molecules will decrease, and the energy released must be dissipated into the environment in the form of heat. At this point, the system continues to be heat-vented, the temperature does not drop, and the water gradually condenses. Water has a very special physical property, that is, it has the highest density at 4, and the density decreases at higher or lower temperatures.

The expansion of water molecules occurs before the water freezes completely, so if the temperature of a pool of lake water is between 0 and 4, then the water density and temperature will be lower in the upper layer, and the water at the bottom of the pool is the densest and the warmest is also the highest4. When the water temperature decreases, the colder water (water between 0 4) rises to the surface of the lake due to its less density and then freezes into solid ice. This layer of ice isolates the water below from the cold air outside, so the water in the lower layer is less likely to freeze, allowing the creatures that live in the lake to survive the harsh winter in the waters below the ice.

So, the icing must start on a cooler surface. So why does the ice move from the periphery to the center?Before talking about the more in-depth answers, we must first explain that cooling water to obtain ice will first produce ice crystals in the process.

At the molecular scale, a water molecule is made up of one oxygen atom and two hydrogen atoms with chemical bonds. Since the outer electron orbital of the oxygen atom is still two electrons away from filling, after the combination of hydrogen and oxygen to form water, the electrons of the two hydrogen atoms will be closer to the nucleus of oxygen, so that the two regions close to the hydrogen nucleus of each water molecule are more positively charged, and the region close to the oxygen nucleus is more negatively charged. Therefore, when two water molecules are close to each other, the regions with different electrical properties will attract each other, reducing the potential energy of each other to form hydrogen bonds, and the original potential energy will be converted into kinetic energy.

If this excess kinetic energy is then transmitted to other nearby water molecules or other molecules through collisions, the hydrogen bond gradually stabilizes;If the new collision gives the pair of water molecules more kinetic energy, the hydrogen bonds are prone to breaking. <>

We drink water, we use it to swim, we use it to bathe, we use it to cool things. Because water is so common, many of us don't notice how strange it is compared to other substances. When we plop the ice and warm it up, pour a cube or two of ice into the cup, and we don't hesitate to watch it float on top of the liquid in the cup.

But why is ice like this? More importantly, why is water frozen from top to bottom, while most other substances are frozen from bottom to top?

The water freezes from top to bottom, which allows the ice to float because the way the water freezes has a strange quirk density that manifests itself at falling temperatures. Density is the unit volume of matter.

quality; It is essentially a measure of atoms and molecules, a foci of a substance. For most compounds, the source temperature drops so that the compound decreases in volume and increases in density – atoms and molecules come together more closely. For example, a bag of warm air rises and expands because it is less dense than the colder air around.

Instead, a cold air bag descends and shrinks, becoming slightly thicker and denser as it falls. Water behaves similarly, but only at a certain temperature. Cooling water.

The density will increase until the water temperature reaches 4°C (. If the water continues to cool, its density will begin to increase again, and the water (now solid) will expand. It is this property of water that allows ice to be able to be used on pavements.

Cracked rocks on the upper wedge lead to cans and bottles of soft drinks in the freezer.

**。At 4°C, the water is still in a liquid state. In lakes and rivers, this water cools at the surface, increases in density, and then falls.

As the water approaches freezing point (0°C [32°F]), it becomes less dense than the surrounding water, and then it rises to the top of the water column. If water freezes from the bottom of a lake or the top of a river, there will be far-reaching ecological consequences. Shallow lakes freeze solid; Unless the plants, animals, and other organisms that live there have some kind of adaptation that keeps their tissues from freezing, they will die.

In larger lakes, ice and silt can cool the water above, potentially slowing the metabolism and the growth rate of organisms that survive in the fluid upstream of the lake. In this case, the Earth would look very different; The polar regions of the planet will be virtually life-free, and every year plants, animals, and other organisms in the mid-latitudes will face the prospect of not having access to liquid water in frozen solid habitats.

Icing means that the substance reaches its three-phase point, which is related to the substance, and is also related to the external environment, such as air pressure.

From the molecular point of view, it is that the vibration of the lattice annihilation at low temperature is not as intense as before, and the average kinetic energy of the molecule is low, so it is bound to the lattice near the vibration mold silver, and to a certain extent, it becomes a solid.

Why does the water in the bucket freeze? And the water in the pool or elsewhere doesn't freeze?

It is because the amount of water in the bucket or basin is too small, once the water is cooled down, the heat is quickly consumed and absorbed, while in the pool and other places where there is a lot of water, it is difficult to consume the heat and still maintain the temperature above zero, so the water in the bucket is easy to freeze. In the same way, the temperature on the seashore is higher than on the land, because the large amount of seawater stores an inexhaustible amount of heat.

Change in density of water after freezing: The density of water becomes less when it freezes. The density of water is, and the density of ice is.

As a result, the density of water freezes smaller. The mass of a certain substance per unit volume is called the density of the substance, and the density is a property of the substance itself, which is related to the type, state and temperature of the substance, and has nothing to do with the mass, volume and shape.

Change in volume after water freezes: Water becomes larger in volume after freezing. Because the mass of water does not change after freezing, but the density becomes smaller, it can be seen from the formula v=m:

The volume becomes larger. The specific reason is that there is a strong hydrogen bonding force between the water molecules in liquid water. It is much greater than the intermolecular forces (van der Waals force).

When water is in a liquid state, under the action of hydrogen bonding force, the water molecules are close together, and it appears to be small in size at the macro level. When it becomes solid, the water becomes crystalline, the arrangement of hundreds of subs becomes regular, the force of hydrogen bonding is weakened, and the macroscopic manifestation becomes larger.

What happens when the water freezes:

1.When water freezes, it changes from a liquid state to a solid state.

2.Increased volume.

The flowing water itself has a certain kinetic energy, so the kinetic energy generally comes from the potential energy, which is the transformation from high flow to low flow.

Why do you think that flowing water can't freeze?

Icing is actually the conversion of liquid to solid state in the change of state of matter, you must first understand how static water is converted into ice, from a macroscopic understanding, in the river, the flow rate of each part is different, then, the speed of the most shore is lower, some water will seep into the soil on the shore, it will not continue to flow, so it freezes at low temperatures.

However, when the weather is cold, that is, the heat of the water can only be taken away by the earth and air, then the water surface is more likely to freeze, then, you can pay attention to the flowing water, the edge begins to freeze, and gradually extends from the water surface to the river**.

As the ice on the banks and on the surface of the river becomes thicker, causing the river to become thinner, it may cause the flow rate to drop or even break off, so that the moving water begins to become still water, and eventually freezes completely.

The above is when the temperature is low enough.

Why do you say that, microscopically, why does water turn into ice? The change of state of matter is due to the change in the distance between molecules, for molecules, different molecules have a certain "pursuit" for "freedom", then, temperature is one of the factors of speed and their freedom, because temperature can give energy to molecules. Once the molecules possess energy, their own molecular movements become so active that the structures between them collapse into each other.

Produce a change in the state of matter.

Conversely, the temperature decreases, weakening the ability of molecules to move, and the ability to attract each other takes over, as a result of which their distance becomes smaller and smaller, and finally reached.

Repulsion = relative static equilibrium of attraction, so that no one can move, and finally, when it comes to the water molecules, they are honest and turn into ice.

For flowing water, in addition to its own molecular motion, there is also kinetic energy converted by gravitational potential energy, so the temperature will be bound by more than just molecular potential energy.

Why does running water not freeze easily? That's because it's not cold enough

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.

The water freezes at zero degrees Celsius, and the surface of the lake freezes because of the low temperature outside, the temperature at the bottom of the lake is higher than the surface of the lake, and the flowing water does not freeze.

In most parts of China, ice formation occurs after the beginning of winter. Winter means the end of the crop, which means that the crops should be collected after harvesting. In ancient China, it was customary to take the beginning of winter as the beginning of winter.

There are three waits for the beginning of winter: one is when the water begins to freeze, that is, the water can already form ice; Second, the land begins to freeze, that is, the land also begins to freeze; The three pheasants enter the water as a mirage, and the pheasant refers to a large bird such as pheasant; Disguise yourself as a mirage, that is, a large clam.

After the beginning of winter, pheasants are rare, but on the seashore you can see large clams with similar lines and colors to pheasants, and the ancients believed that pheasants became big clams after the beginning of winter.

In winter, the temperature decreases, and due to heat transfer, the temperature of the river surface is consistent with the outside temperature, and convection is formed due to the flow of water, so that the temperature inside the water also remains the same. When the single temperature drops below 4 degrees, the temperature of the river surface also decreases, but due to the anti-expansion of the water, the density also becomes smaller, and it no longer sinks, so that the water inside the river can not form convection, and the water inside the river can still maintain 4 degrees, and the river surface continues to cool down until 0 degrees, begins to freeze, and continues to cool down, the temperature on the surface of the ice is consistent with the outside world, but because the ice is a bad conductor of heat, the lower surface of the ice quietly maintains 0 degrees. The water under the ice does not freeze, it still flows, and the higher you go, the cooler it gets.