In the good old formula H 2 O, it would seem that there are no secrets. But in fact, water - the source of life and the most famous liquid in the world - is fraught with many mysteries that sometimes even scientists cannot solve.
Here are the 5 most interesting facts about water:
1. Hot water freezes faster than cold water
Take two containers of water: pour hot water into one and cold water into the other, and place them in the freezer. Hot water will freeze faster than cold water, although logically, cold water should have turned into ice first: after all, hot water must first cool down to cold temperature, and then turn into ice, while cold water no need to cool down. Why is this happening?
In 1963, Erasto B. Mpemba, high school student high school in Tanzania, when freezing a prepared ice cream mix, I noticed that the hot mix hardens faster in the freezer than the cold one. When the young man shared his discovery with a physics teacher, he only laughed at him. Fortunately, the student was persistent and persuaded the teacher to conduct an experiment, which confirmed his discovery: in certain conditions hot water really freezes faster than cold.
Now this phenomenon of hot water freezing faster than cold water is called the Mpemba effect. True, long before it unique property water was noted by Aristotle, Francis Bacon and Rene Descartes.
Scientists do not fully understand the nature of this phenomenon, explaining it either by the difference in hypothermia, evaporation, ice formation, convection, or the effect of liquefied gases on hot and cold water.
Note from Х.RU to the topic "Hot water freezes faster than cold water".
Since the issues of cooling are closer to us, refrigerators, we will allow ourselves to go deeper into the essence of this problem and give two opinions about the nature of such mysterious phenomenon.
1. A University of Washington scientist has offered an explanation for a mysterious phenomenon known since the time of Aristotle: why hot water freezes faster than cold water.
The phenomenon, called the Mpemba effect, is widely used in practice. For example, experts advise motorists to pour cold rather than hot water into the washer reservoir in winter. But what underlies this phenomenon? for a long time remained unknown.
Dr. Jonathan Katz of the University of Washington investigated this phenomenon and concluded that important role it is played by substances dissolved in water, which precipitate when heated, according to EurekAlert.
Under dissolved substances dr Katz refers to the calcium and magnesium bicarbonates found in hard water. When the water is heated, these substances precipitate, forming scale on the walls of the kettle. Water that has never been heated contains these impurities. As it freezes and ice crystals form, the concentration of impurities in water increases 50 times. This lowers the freezing point of water. "And now the water has to cool down in order to freeze," explains Dr. Katz.
There is a second reason that prevents freezing of unheated water. Lowering the freezing point of water reduces the temperature difference between the solid and liquid phases. "Because the rate at which water loses heat depends on this temperature difference, water that has not been heated is less likely to cool down," says Dr. Katz.
According to the scientist, his theory can be tested experimentally, because. the Mpemba effect becomes more pronounced for harder water.
2. Oxygen plus hydrogen plus cold creates ice. At first glance, this transparent substance seems very simple. In fact, the ice is fraught with many mysteries. The ice created by the African Erasto Mpemba did not think about glory. The days were hot. He wanted fruit ice. He took a carton of juice and put it in the freezer. He did this more than once and therefore noticed that the juice freezes especially quickly, if you hold it in the sun before that - just heat it up! This is strange, thought the Tanzanian schoolboy, who acted contrary to worldly wisdom. Is it possible that in order for the liquid to turn into ice faster, it must first ... be heated? The young man was so surprised that he shared his guess with the teacher. He reported this curiosity in the press.
This story happened back in the 1960s. Now the "Mpemba effect" is well known to scientists. But for a long time this seemingly simple phenomenon remained a mystery. Why does hot water freeze faster than cold water?
It wasn't until 1996 that physicist David Auerbach found a solution. To answer this question, he conducted an experiment for a whole year: he heated water in a glass and cooled it again. So what did he find out? When heated, air bubbles dissolved in water evaporate. Water devoid of gases freezes more easily on the walls of the vessel. "Of course, water with a high air content will also freeze," says Auerbach, "but not at zero degrees Celsius, but only at minus four to six degrees." Of course, you will have to wait longer. So, hot water freezes before cold water, this is a scientific fact.
There is hardly a substance that would appear before our eyes with the same ease as ice. It consists only of water molecules - that is, elementary molecules containing two hydrogen atoms and one oxygen. However, ice is perhaps the most mysterious substance in the universe. Scientists have not been able to explain some of its properties so far.
2. Supercooling and "flash" freezing
Everyone knows that water always turns to ice when it cools down to 0 °C... except in some cases! Such a case, for example, is "supercooling", which is a property of very clean water remain liquid even when chilled below freezing. This phenomenon is made possible by the fact that environment does not contain centers or nuclei of crystallization, which could provoke the formation of ice crystals. And so water remains in liquid form, even when cooled to temperatures below zero degrees Celsius. The crystallization process can be triggered, for example, by gas bubbles, impurities (pollution), uneven surface of the container. Without them, the water will remain in liquid state. When the crystallization process starts, you can watch how the super-cooled water instantly turns into ice.
Watch the video (2 901 Kb, 60 c) by Phil Medina (www.mrsciguy.com) and see for yourself >>
Comment. Superheated water also remains liquid even when heated above its boiling point.
3. "Glass" water
Quickly and without hesitation, name how much different states does the water have?
If you answered three (solid, liquid, gas), then you are wrong. Scientists distinguish at least 5 different states of water in liquid form and 14 states of ice.
Remember the conversation about super-chilled water? So, no matter what you do, at -38 ° C, even the purest super-cooled water suddenly turns into ice. What happens with a further decrease
temperature? At -120 °C, something strange begins to happen to water: it becomes super-viscous or viscous, like molasses, and at temperatures below -135 °C it turns into "glassy" or "glassy" water - a solid substance in which there is no crystalline structure.
4. Quantum properties of water
At the molecular level, water is even more surprising. In 1995, a neutron scattering experiment conducted by scientists gave an unexpected result: physicists found that neutrons directed at water molecules “see” 25% fewer hydrogen protons than expected.
It turned out that at the speed of one attosecond (10 -18 seconds) an unusual quantum effect takes place, and chemical formula water instead of the usual - H 2 O, becomes H 1.5 O!
5. Does water have a memory?
Homeopathy, an alternative to conventional medicine, claims that a dilute solution medicinal product can have a therapeutic effect on the body, even if the dilution factor is so large that there is nothing left in the solution but water molecules. Proponents of homeopathy explain this paradox with a concept called "memory of water", according to which water at the molecular level has a "memory" of the substance once dissolved in it and retains the properties of the solution of the original concentration after not a single molecule of the ingredient remains in it.
An international team of scientists led by Professor Madeleine Ennis from Queen's University of Belfast, who criticized the principles of homeopathy, conducted an experiment in 2002 to disprove this concept once and for all. The result was the opposite. After which, scientists said that they were able to prove the reality of the effect of "memory of water. However, experiments conducted under the supervision of independent experts, did not bring results. Disputes about the existence of the phenomenon of "memory of water" continue.
Water has many other unusual properties which we have not covered in this article.
Literature.
1. 5 Really Weird Things About Water / http://www.neatorama.com.
2. The mystery of water: the theory of the Aristotle-Mpemba effect was created / http://www.o8ode.ru.
3. Nepomniachtchi N.N. Secrets of inanimate nature. The most mysterious substance in the universe / http://www.bibliotekar.ru.
Mpemba effect(Mpemba paradox) - a paradox that states that hot water under certain conditions freezes faster than cold water, although it must pass the temperature of cold water in the process of freezing. This paradox is an experimental fact that contradicts the usual ideas, according to which, under the same conditions, a hotter body needs more time to cool down to a certain temperature than a cooler body to cool down to the same temperature.
This phenomenon was noticed at the time by Aristotle, Francis Bacon and Rene Descartes, but only in 1963, the Tanzanian schoolboy Erasto Mpemba found that a hot ice cream mixture freezes faster than a cold one.
As a student at the Magamba High School in Tanzania, Erasto Mpemba did practical work in the culinary arts. He had to make homemade ice cream - boil milk, dissolve sugar in it, cool it to room temperature and then place in the refrigerator to freeze. Apparently, Mpemba was not a particularly diligent student and procrastinated on the first part of the assignment. Fearing that he would not be in time by the end of the lesson, he put the still hot milk in the refrigerator. To his surprise, it froze even earlier than the milk of his comrades, prepared according to a given technology.
After that, Mpemba experimented not only with milk, but also with ordinary water. In any case, already being a student of Mkvava High School, he asked a question to Professor Dennis Osborn from university college in Dar es Salaam (invited by the director of the school to give a lecture on physics to students) about water: "If you take two identical containers with equal volumes of water so that in one of them the water has a temperature of 35 ° C, and in the other - 100 ° C, and put them in the freezer, then in the second the water will freeze faster. Why?" Osborne became interested in this issue and soon in 1969, together with Mpemba, they published the results of their experiments in the journal "Physics Education". Since then, the effect they discovered is called Mpemba effect.
Until now, no one knows exactly how to explain this strange effect. Scientists do not have a single version, although there are many. It's all about the difference in the properties of hot and cold water, but it is not yet clear which properties play a role in this case: the difference in supercooling, evaporation, ice formation, convection, or the effect of liquefied gases on water at different temperatures.
The paradox of the Mpemba effect is that the time during which the body cools down to the ambient temperature must be proportional to the temperature difference between this body and the environment. This law was established by Newton and since then has been confirmed many times in practice. In the same effect, water at 100°C cools down to 0°C faster than the same amount of water at 35°C.
However, this does not yet imply a paradox, since the Mpemba effect can also be explained within known physics. Here are some explanations for the Mpemba effect:
Evaporation
Hot water evaporates faster from the container, thereby reducing its volume, and a smaller volume of water with the same temperature freezes faster. Water heated to 100 C loses 16% of its mass when cooled to 0 C.
The evaporation effect is a double effect. First, the mass of water required for cooling is reduced. And secondly, the temperature decreases due to the fact that the heat of evaporation of the transition from the water phase to the vapor phase decreases.
temperature difference
Due to the fact that the temperature difference between hot water and cold air is greater - hence the heat exchange in this case is more intense and hot water cools faster.
hypothermia
When water is cooled below 0 C, it does not always freeze. Under certain conditions, it can undergo supercooling while continuing to remain liquid at temperatures below the freezing point. In some cases, water can remain liquid even at -20 C.
The reason for this effect is that in order for the first ice crystals to begin to form, centers of crystal formation are needed. If they are not in liquid water, then supercooling will continue until the temperature drops enough that crystals begin to form spontaneously. When they start to form in the supercooled liquid, they will start to grow faster, forming an ice slush that will freeze to form ice.
Hot water is most susceptible to hypothermia because heating it eliminates dissolved gases and bubbles, which in turn can serve as centers for the formation of ice crystals.
Why does hypothermia cause hot water to freeze faster? In case of cold water, which is not supercooled, the following occurs. In this case, a thin layer of ice will form on the surface of the vessel. This layer of ice will act as an insulator between the water and cold air and will prevent further evaporation. The rate of formation of ice crystals in this case will be less. In the case of hot water undergoing subcooling, the subcooled water does not have a protective surface layer of ice. Therefore, it loses heat much faster through the open top.
When the supercooling process ends and the water freezes, much more heat is lost and therefore more ice is formed.
Many researchers of this effect consider hypothermia to be the main factor in the case of the Mpemba effect.
Convection
Cold water begins to freeze from above, thereby worsening the processes of heat radiation and convection, and hence the loss of heat, while hot water begins to freeze from below.
This effect is explained by an anomaly in the density of water. Water has a maximum density at 4 C. If you cool water to 4 C and put it at a lower temperature, the surface layer of water will freeze faster. Because this water is less dense than water at 4°C, it will stay on the surface, forming a thin cold layer. Under these conditions, a thin layer of ice will form on the surface of the water for a short time, but this layer of ice will serve as an insulator protecting the lower layers of water, which will remain at a temperature of 4 C. Therefore, the further cooling process will be slower.
In the case of hot water, the situation is completely different. The surface layer of water will cool more rapidly due to evaporation and more difference temperatures. Also, cold water layers are denser than hot water layers, so the cold water layer will sink down, raising the layer. warm water to the surface. This circulation of water ensures a rapid drop in temperature.
But why does this process not reach the equilibrium point? To explain the Mpemba effect from this point of view of convection, one would have to assume that the cold and hot layers of water are separated and the convection process itself continues after the average water temperature drops below 4 C.
However, there is no experimental evidence to support this hypothesis that cold and hot layers of water are separated by convection.
gases dissolved in water
Water always contains gases dissolved in it - oxygen and carbon dioxide. These gases have the ability to lower the freezing point of water. When the water is heated, these gases are released from the water because their solubility in water at high temperature below. Therefore, when hot water is cooled, there are always fewer dissolved gases in it than in unheated cold water. Therefore, the freezing point of heated water is higher and it freezes faster. This factor is sometimes considered as the main one in explaining the Mpemba effect, although there are no experimental data confirming this fact.
Thermal conductivity
This mechanism can play a significant role when water is placed in a refrigerator freezer in small containers. Under these conditions, it has been observed that the container with hot water melts the ice of the freezer underneath, thereby improving thermal contact with the wall of the freezer and thermal conductivity. As a result, heat is removed from the hot water container faster than from the cold one. In turn, the container with cold water does not melt snow under it.
All these (as well as other) conditions have been studied in many experiments, but an unequivocal answer to the question - which of them provide a 100% reproduction of the Mpemba effect - has not been obtained.
So, for example, in 1995, the German physicist David Auerbach studied the influence of supercooling of water on this effect. He discovered that hot water, reaching a supercooled state, freezes at a higher temperature than cold water, and therefore faster than the latter. But cold water reaches the supercooled state faster than hot water, thereby compensating for the previous lag.
In addition, Auerbach's results contradicted earlier data that hot water is able to achieve greater supercooling due to fewer crystallization centers. When water is heated, the gases dissolved in it are removed from it, and when it is boiled, some salts dissolved in it precipitate.
So far, only one thing can be asserted - the reproduction of this effect essentially depends on the conditions under which the experiment is carried out. Precisely because it is not always reproduced.
O. V. Mosin
Literarysources:
"Hot water freezes faster than cold water. Why does it do so?", Jearl Walker in The Amateur Scientist, Scientific American, Vol. 237, no. 3, pp. 246-257; September, 1977.
"The Freezing of Hot and Cold Water", G.S. Kell in American Journal of Physics, Vol. 37, no. 5, pp. 564-565; May 1969.
"Supercooling and the Mpemba effect", David Auerbach, in American Journal of Physics, Vol. 63, no. 10, pp. 882-885; Oct, 1995.
"The Mpemba effect: The freezing times of hot and cold water", Charles A. Knight, in American Journal of Physics, Vol. 64, no. 5, p 524; May, 1996.
Which water freezes faster, hot or cold, is influenced by many factors, but the question itself seems a little strange. It is understood, and it is known from physics, that hot water still needs time to cool down to the temperature of comparable cold water in order to turn into ice. Cold water can skip this stage, and, accordingly, it wins in time.
But the answer to the question of which water freezes faster - cold or hot - on the street in frost, any resident knows northern latitudes. In fact, scientifically, it turns out that in any case, cold water simply has to freeze faster.
So did the teacher of physics, who was approached by the schoolboy Erasto Mpemba in 1963 with a request to explain why the cold mixture of future ice cream freezes longer than a similar, but hot one.
"This is not world physics, but some kind of Mpemba physics"
At that time, the teacher only laughed at this, but Deniss Osborne, a professor of physics, who at one time went to the same school where Erasto studied, experimentally confirmed the existence of such an effect, although there was no explanation for this then. In 1969, in the popular scientific journal published a joint article of these two people who described this peculiar effect.
Since then, by the way, the question of which water freezes faster - hot or cold, has its own name - the effect, or paradox, Mpemba.
The question has been around for a long time
Naturally, such a phenomenon has taken place before, and it was mentioned in the works of other scientists. Not only the schoolboy was interested in this question, but Rene Descartes and even Aristotle thought about it at one time.
Here are just approaches to solving this paradox began to look only at the end of the twentieth century.
Conditions for a paradox to occur
As with ice cream, it's not just ordinary water that freezes during the experiment. Certain conditions must be present in order to start arguing which water freezes faster - cold or hot. What influences this process?
Now, in the 21st century, several options have been put forward that can explain this paradox. Which water freezes faster, hot or cold, may depend on the fact that it has a higher evaporation rate than cold water. Thus, its volume decreases, and with a decrease in volume, the freezing time becomes shorter than if we take a similar initial volume of cold water.
Freezer has long been defrosted
Which water freezes faster, and why it does so, can be affected by the snow lining that may be present in the freezer of the refrigerator used for the experiment. If you take two containers that are identical in volume, but one of them will have hot water and the other cold water, the container with hot water will melt the snow underneath, thereby improving the contact of the thermal level with the refrigerator wall. A cold water container can't do that. If there is no such lining with snow in the refrigerator, cold water should freeze faster.
Top - bottom
Also, the phenomenon of which water freezes faster - hot or cold, is explained as follows. Following certain laws, cold water starts to freeze from the upper layers, when hot water does it the other way around - it starts to freeze from the bottom up. At the same time, it turns out that cold water, having a cold layer on top with ice already formed in places, thus impairs convection processes and thermal radiation, thereby explaining which water freezes faster - cold or hot. A photo from amateur experiments is attached, and here it is clearly visible.
The heat goes out, tending upwards, and there it meets a very cool layer. There is no free path for heat radiation, so the cooling process becomes difficult. Hot water has absolutely no such barriers in its path. Which freezes faster - cold or hot, on which the probable outcome depends, you can expand the answer by saying that any water has certain substances dissolved in it.
Impurities in the composition of water as a factor influencing the outcome
If you do not cheat and use water with the same composition, where the concentrations of certain substances are identical, then cold water should freeze faster. But if a situation occurs when the dissolved chemical elements available only in hot water, while cold water does not have them, then there is a possibility for hot water to freeze earlier. This is explained by the fact that dissolved substances in water create crystallization centers, and with a small number of these centers, the transformation of water into solid state difficult. Even supercooling of water is possible, in the sense that at sub-zero temperatures it will be in a liquid state.
But all these versions, apparently, did not suit the scientists to the end, and they continued to work on this issue. In 2013, a team of researchers in Singapore said they had solved the age-old mystery.
A group of Chinese scientists claim that the secret this effect consists in the amount of energy that is stored between water molecules in its bonds, called hydrogen bonds.
The answer from Chinese scientists
Further information will follow, for the understanding of which it is necessary to have some knowledge in chemistry in order to figure out which water freezes faster - hot or cold. As you know, it consists of two H (hydrogen) atoms and one O (oxygen) atom held together by covalent bonds.
But hydrogen atoms of one molecule are also attracted to neighboring molecules, to their oxygen component. These bonds are called hydrogen bonds.
At the same time, it is worth remembering that at the same time, water molecules act repulsively on each other. Scientists noted that when water is heated, the distance between its molecules increases, and this is facilitated by repulsive forces. It turns out that occupying one distance between molecules in a cold state, one can say that they stretch, and they have a greater supply of energy. It is this energy reserve that is released when water molecules begin to approach each other, that is, cooling occurs. It turns out that a larger supply of energy in hot water, and its greater release when cooled to sub-zero temperatures, occurs faster than in cold water, which has a smaller supply of such energy. So which water freezes faster - cold or hot? On the street and in the laboratory, the Mpemba paradox should occur, and hot water should turn into ice faster.
But the question is still open
There is only theoretical confirmation of this clue - all this is written in beautiful formulas and seems plausible. But when the experimental data, which water freezes faster - hot or cold, will be put in a practical sense, and their results will be presented, then it will be possible to consider the question of the Mpemba paradox closed.
Chemistry was one of my favorite subjects in school. Once a chemistry teacher gave us a very strange and difficult task. He gave us a list of questions that we had to answer in terms of chemistry. We were given several days for this task and were allowed to use libraries and other available sources of information. One of these questions concerned the freezing point of water. I don't remember exactly how the question sounded, but it was about the fact that if you take two wooden buckets of the same size, one with hot water, the other with cold water (at exactly the specified temperature), and place them in an environment with a certain temperature, which one will they freeze faster? Of course, the answer immediately suggested itself - a bucket of cold water, but it seemed to us too simple. But this was not enough to give a complete answer, we needed to prove it from a chemical point of view. Despite all my thought and research, I have not been able to inference. On this day, I even decided to skip this lesson, so I never found out the solution to this riddle.
Years passed, and I learned a lot of everyday myths about the boiling point and freezing point of water, and one myth said: "hot water freezes faster." I looked at many websites but the information was too conflicting. And these were just opinions, unfounded from the point of view of science. And I decided to take own experience. Since I couldn't find wooden buckets, I used a freezer, stovetop, some water, and a digital thermometer. I will talk about the results of my experience a little later. First, I will share with you some interesting arguments about water:
Hot water freezes faster than cold water. Most experts say that cold water will freeze faster than hot water. But one funny phenomenon (the so-called Memba effect), according to unknown reasons, proves the opposite: Hot water freezes faster than cold water. One of several explanations is the evaporation process: if very hot water is placed in a cold environment, then the water will begin to evaporate (the remaining amount of water will freeze faster). And according to the laws of chemistry, this is not a myth at all, and most likely this is what the teacher wanted to hear from us.
Boiled water freezes faster tap water. Despite the previous explanation, some experts argue that boiled water, cooled to room temperature, should freeze faster, because as a result of boiling, the amount of oxygen is reduced.
Cold water boils faster than hot water. If hot water freezes faster, then cold water may boil faster! This is contrary to common sense and scientists argue that this simply cannot be. Hot tap water should actually boil faster than cold water. But by using hot water to boil, you don't save energy. You may use less gas or electricity, but the water heater will use the same amount of energy that is needed to heat cold water. (Solar power is a little different.) As a result of heating the water with a water heater, sediment may form, so the water will take longer to heat up.
If you add salt to water, it will boil faster. Salt increases the boiling point (and therefore lowers the freezing point - which is why some housewives add a little rock salt to ice cream). But us in this case another question is of interest: how long will the water boil and whether the boiling point in this case can rise above 100 ° C). Despite what cookbooks say, scientists say that the amount of salt we add to boiling water is not enough to affect the time or temperature of the boil.
But here's what I got:
Cold water: I used three 100 ml glass beakers of purified water: one room temperature (72°F/22°C), one hot water (115°F/46°C), and one boiled (212 °F/100°C). I placed all three glasses in the freezer at -18°C. And since I knew that water would not immediately turn into ice, I determined the degree of freezing by the “wooden float”. When the stick, placed in the center of the glass, no longer touched the base, I believed that the water had frozen. I checked the glasses every five minutes. And what are my results? The water in the first glass froze after 50 minutes. Hot water froze after 80 minutes. Boiled - after 95 minutes. My Conclusions: Considering the conditions in the freezer and the water I used, I was unable to reproduce the Memba effect.
I also tried this experiment with previously boiled water cooled to room temperature. It froze in 60 minutes - it still took longer than cold water to freeze.
Boiled water: I took a liter of water at room temperature and put it on fire. She boiled in 6 minutes. Then I cooled it down to room temperature again and added it to the hot one. With the same fire, hot water boiled in 4 hours and 30 minutes. Conclusion: as expected, hot water boils much faster.
Boiled water (with salt): I added 2 large tablespoons of table salt to 1 liter of water. It boiled in 6 minutes 33 seconds, and as the thermometer showed it reached a temperature of 102°C. Undoubtedly, salt affects the boiling point, but not much. Conclusion: salt in water does not greatly affect the temperature and boiling time. I honestly admit that my kitchen is hard to call a laboratory, and perhaps my conclusions are contrary to reality. My freezer may freeze food unevenly. My glass glasses could be irregular shape, Etc. But whatever happens in the laboratory, when we are talking about freezing or boiling water in the kitchen, the most important thing is common sense.
link from interesting facts about waterall about water
as suggested on the forum.ixbt.com forum, this effect (the effect of freezing hot water faster than cold water) is called the "Aristotle-Mpemba effect"
Those. boiled water (chilled) freezes faster than "raw"
Water- a fairly simple substance from a chemical point of view, however, it has a number of unusual properties that never cease to amaze scientists. Below are some facts that few people know about.
1. Which water freezes faster - cold or hot?
Take two containers of water: pour hot water into one and cold water into the other, and place them in the freezer. Hot water will freeze faster than cold water, although logically, cold water should have turned into ice first: after all, hot water must first cool down to cold temperature, and then turn into ice, while cold water does not need to cool down. Why is this happening?
In 1963, a Tanzanian student named Erasto B. Mpemba, while freezing a prepared ice cream mixture, noticed that the hot mixture solidified faster in the freezer than the cold one. When the young man shared his discovery with a physics teacher, he only laughed at him. Fortunately, the student was persistent and convinced the teacher to conduct an experiment, which confirmed his discovery: under certain conditions, hot water really freezes faster than cold water.
Now this phenomenon of hot water freezing faster than cold water is called " Mpemba effect". True, long before him, this unique property of water was noted by Aristotle, Francis Bacon and Rene Descartes.
Scientists do not fully understand the nature of this phenomenon, explaining it either by the difference in hypothermia, evaporation, ice formation, convection, or the effect of liquefied gases on hot and cold water.
2. She is able to freeze instantly
Everyone knows that water always turns to ice when cooled to 0 °C ... except in some cases! Such a case is, for example, supercooling, which is the property of very pure water to remain liquid even when cooled to a temperature below freezing. This phenomenon becomes possible due to the fact that the environment does not contain crystallization centers or nuclei that could provoke the formation of ice crystals. And so water remains in liquid form, even when cooled to temperatures below zero degrees Celsius.
crystallization process can be provoked, for example, by gas bubbles, impurities (pollution), uneven surface of the container. Without them, water will remain in a liquid state. When the crystallization process starts, you can watch how the super-cooled water instantly turns into ice.
Note that "superheated" water also remains liquid even when heated above its boiling point.
3. 19 states of water
Without hesitation, name how many different states water has? If you answered three: solid, liquid, gaseous, then you are mistaken. Scientists distinguish at least 5 different states of water in liquid form and 14 states in frozen form.
Remember the conversation about super-chilled water? So, no matter what you do, at -38 ° C, even the purest super-cooled water will suddenly turn into ice. What happens as the temperature drops further? At -120°C, something strange begins to happen to water: it becomes super-viscous or viscous, like molasses, and at temperatures below -135°C, it turns into "glassy" or "glassy" water - a solid that lacks crystalline structure.
4. Water surprises physicists
At the molecular level, water is even more surprising. In 1995, a neutron scattering experiment conducted by scientists gave an unexpected result: physicists found that neutrons directed at water molecules “see” 25% fewer hydrogen protons than expected.
It turned out that at the speed of one attosecond (10 -18 seconds) an unusual quantum effect takes place, and the chemical formula of water instead of H2O, becomes H1.5O!
5. Water memory
Alternative to official medicine homeopathy argues that a dilute solution of a drug can have a therapeutic effect on the body, even if the dilution factor is so large that there is nothing left in the solution but water molecules. Proponents of homeopathy explain this paradox with a concept called " water memory”, according to which water at the molecular level has a “memory” of a substance once dissolved in it and retains the properties of a solution of the initial concentration after not a single ingredient molecule remains in it.
An international team of scientists led by Professor Madeleine Ennis of Queen's University of Belfast, who criticized the principles of homeopathy, conducted an experiment in 2002 to disprove the concept once and for all. The result was the opposite. After that, scientists said that they managed to prove the reality of the effect " water memory". However, experiments conducted under the supervision of independent experts did not bring results. Disputes about the existence of the phenomenon " water memory» continue.
Water has many other unusual properties that we have not covered in this article. For example, the density of water varies with temperature (the density of ice is less than that of water); water has a fairly large surface tension; in a liquid state, water is a complex and dynamically changing network of water clusters, and it is the behavior of clusters that affects the structure of water, etc.
About these and many other unexpected features water can be read in the article Anomalous properties of water”, the author of which is Martin Chaplin, professor at the University of London.
