water is very ordinary, small cell, large ocean, there is the presence of water; water is very unusual, water, bathing, water the plants …… life in bits and pieces have water involved.
But the water is strange. The general object will be “thermal expansion and contraction”. Sometimes the water is “cold expansion and contraction”. The density of water at 4 °C is greater than the density of ice. The specific heat ratio of water is mostly The material is large and the heat absorption capacity is extremely strong; the water has a good carrying capacity and is the best solvent to dissolve many substances.
These peculiarities of water are meaningful. If the water density at low temperature is smaller than that of ice, then in winter, the water of lakes and rivers will freeze from the bottom layer, and the creatures in the water will have no place to stand. If the specific heat capacity of the water is not so large and does not absorb a lot of heat, then the summer lakes and oceans will probably be boiling; if the water does not have a strong dissolving power, it will not be able to transport the nutrients it needs for the cells.
In short, water is peculiar, and its peculiarity is what we need. But why is water so strange? This problem has plagued scientists, and its research can be traced back to the era of Galileo, but at the time it was nothing. Recently, some scientists have given a new explanation for this. This explanation is as strange as water: in fact, water is not a liquid, but two.
The second critical point
of water in three forms: a gaseous, liquid and solid, which is in the form depends on the temperature and pressure. For example, in the plains, when the water is heated to 100 ° C, it will boil and form water vapor. In the Qinghai-Tibet Plateau, where the pressure is lower than that in the plain, the water is heated to about 90 ° C, and it boils.
In general, liquid and gaseous water are well differentiated and visible to the naked eye. But if you change the pressure and temperature, the situation will change. The temperature is constant, the pressure is reduced, and the liquid water is gradually converted into gaseous water. For example, water at 90 °C becomes gaseous water on the Qinghai-Tibet Plateau with a small pressure. The pressure is constant, the temperature is raised, and the liquid water is converted into gaseous water. In the process of mutual transformation of two forms of water, there is always a transition point at which water will exhibit both the nature of liquid water and the nature of gas water. Distinguish, after this point, it will become a non-liquid state. This point is called the “critical point.” For example, at standard atmospheric pressure, 0 ° C is the “critical point” of water changing from solid to liquid, and 100 ° C is the “critical point” of water changing from liquid to gas.
Almost all substances have a critical point of gas-liquid conversion, while some special substances have a “second critical point.” For example, by cooling a mixture of liquid silicon and liquid helium under specific conditions, a mixed liquid composed of two liquids having different densities can be obtained. The peculiarity is that the constituent atoms of the two liquids having different densities are the same. However, the structure is different and thus the properties are different. The point at which this mixture of liquid silicon and liquid helium exhibits this property is the “second critical point”.
However, if you don’t specialize in liquid silicon or liquid helium, you probably won’t be interested in it. The same is true for scientists, who did not care about this area. Until 1992, researchers at Boston University began to focus a lot on the “second critical point”. There is also a second critical point for the liquid state. At the second critical point, the water exhibits the properties of the two liquids. In other words, the water has two liquid phases.
In 1992, when researchers at Boston University experimented, they stumbled upon the pressure. When the temperature was low, the density of water became smaller, and the lower the temperature, the lower the density of water. This situation is very unusual. Generally, the lower the temperature, the less active the material molecules are and the higher the density. In order to explore what happened to the water in this situation, the researchers used a computer to do a simulation experiment. They simulate changes in water in a subcooled state, which refers to liquid water at temperatures below zero degrees Celsius. As a result, it was found that the pressure was constant, the density of water did become smaller as the temperature was lowered, and the density of water showed a large change when the temperature drastically decreased.
For this change in density, they give an explanation that there is a second critical point when water changes from solid to liquid. According to computer simulations, they judge that at standard atmospheric pressure, the second critical point of water is likely to be minus 45 °C. . At this critical point, water consists of two “water”s of different density, like a mixture of liquid silicon and liquid helium. At this critical point, the water molecules have two different arrangements, so that liquid water appears. The state in which the two densities coexist.
This kind of explanation is subversive. Of course, there are many people who are skeptical. Some people think that the traditional view can explain this strange phenomenon. For example, under low temperature conditions, water actually becomes a disorderly solid, or This is the struggle of water before solidification, a special solidification process.
At the time, Boston University’s research team adhered to its own theory, but could not prove their point of view with real experiments, because in the reality outside the computer, it is almost impossible to see the liquid solid state under the condition of water at minus 45 °C. A phenomenon in which the form cannot be distinguished, that is, the state of the supercooled water. The theory that “water is two liquids” seems to have entered a desperate situation.
Water is the two liquids
but there are still people who adhere to this theory, Nelson Stockholm University in Sweden is one of them. Nielsen, obsessed with researching water, combined his data on water experiments he has done under normal temperature and pressure for many years. He suggested that water does have two different liquids, one of which is disordered and dense, and the other is water. The species is a regular tetrahedral structure with a low density. At normal temperature and pressure, low-density water molecules are randomly embedded in high-density water molecules, but it is impossible to see this phenomenon. In the voice of everyone’s doubts, Nielsen decided to experiment to let everyone see the second critical point of water. In 2017, he went to South Korea and used the most advanced technology to produce ultra-pure liquid water. It was proved by experiments that there are two different densities of water at the same pressure and the same temperature. They excitedly announced that they found water. The second critical point.
The outside world is amazed at the advanced technology in this experiment, and many people agree with Nielsen’s experimental results, but some people have raised doubts that the object recorded in the experiment is water droplets, and the volume of water droplets changes little during the whole process. There are many explanations for this tiny volume change, and the second critical point is just one of them. Nelson chose this interpretation just to suit his vision.
Research on the theory that “water is two liquids” continues.
Out of the lab
if “Water is the two liquids” is correct, what is it? In fact, what is closely related to us is not the cold water, but the water under normal temperature and pressure. If the theory of “water is two liquids” is correct, it means that there are two kinds of water in the water under normal temperature and pressure. The state of coexistence, although we can not observe. So, when the theory goes out of the laboratory, can it be related to life?
Scientists believe that water is two kinds of liquids. This seemingly strange theory can explain the anomalies of water around us. For example, why is water denser than ice at 4 °C? Under normal pressure, if the water is changed from 4°C to 0°C, at the microscopic scale, the originally disordered water molecules gradually change from a disordered state to a regular state. According to the above theory, low temperature At the time, the water density in the disordered state is greater, and it is apparent that the density is greater at 4 °C.
I believe that in the future, more water puzzles will be solved.