In 1963, a Tanzanian schoolboy named Erasto Mpemba asked his teacher a stupid question - why did the warm ice cream in his freezer freeze faster than the cold one?
Being a student of Magambinskaya high school in Tanzania Erasto Mpemba did practical work in cooking. He needed to make homemade ice cream - boil milk, dissolve sugar in it, cool it to room temperature, and then put it in the refrigerator to freeze. Apparently, Mpemba was not a particularly diligent student and delayed completing the first part of the task. Fearing that he would not make it by the end of the lesson, he put still hot milk in the refrigerator. To his surprise, it froze even earlier than the milk of his comrades, prepared according to the given technology.
He turned to the physics teacher for clarification, but he only laughed at the student, saying the following: “This is not universal physics, but Mpemba physics.” After this, Mpemba experimented not only with milk, but also with ordinary water.
In any case, already as a student at Mkwava Secondary School, he asked Professor Dennis Osborne from the University College in Dar Es Salaam (invited by the school director to give a lecture on physics to the students) specifically 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, he and Mpemba published the results of their experiments in the journal Physics Education. Since then, the effect they discovered has been called the Mpemba effect.
Are you interested in knowing why this happens? Just a few years ago, scientists managed to explain this phenomenon...
The Mpemba effect (Mpemba Paradox) is a paradox that states that hot water Under some conditions it freezes faster than cold water, although it must pass the temperature of cold water during the freezing process. This paradox is an experimental fact that contradicts the usual ideas, according to which, under the same conditions, a more heated body takes more time to cool to a certain temperature than a less heated body to cool to the same temperature.
This phenomenon was noticed in their time by Aristotle, Francis Bacon and Rene Descartes. 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 a body cools down to the ambient temperature should be proportional to the temperature difference between this body and the environment. This law was established by Newton and has since been confirmed many times in practice. In this effect, water with a temperature of 100°C cools to a temperature of 0°C faster than the same amount of water with a temperature of 35°C.
Since then they have spoken out different versions, one of which sounded as follows: part of the hot water first simply evaporates, and then, when less of it remains, the water freezes faster. This version, due to its simplicity, became the most popular, but did not completely satisfy scientists.
Now a team of researchers from Nanyang Technological University in Singapore, led by chemist Xi Zhang, says they have solved the age-old mystery of why warm water freezes faster than cold water. As Chinese experts have found out, the secret lies in the amount of energy stored in hydrogen bonds between water molecules.
As you know, water molecules consist of one oxygen atom and two hydrogen atoms held together by covalent bonds, which at the particle level looks like an exchange of electrons. Another well-known fact is that hydrogen atoms are attracted to oxygen atoms from neighboring molecules - hydrogen bonds are formed.
At the same time, water molecules generally repel each other. Scientists from Singapore noticed: the warmer the water, the greater the distance between the molecules of the liquid due to an increase in repulsive forces. As a result, hydrogen bonds are stretched and therefore store more energy. This energy is released when the water cools - the molecules move closer to each other. And the release of energy, as is known, means cooling.
Here are the assumptions put forward by scientists:
Evaporation
Hot water evaporates faster from the container, thereby reducing its volume, and a smaller volume of water at 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. Firstly, the mass of water required for cooling decreases. And secondly, due to evaporation, its temperature decreases.
Temperature difference
Due to the temperature difference between hot water and more cold air - therefore, heat exchange in this case is more intense and hot water cools faster.
Hypothermia
When water cools below 0°C it does not always freeze. Under some conditions, it can undergo supercooling, continuing to remain liquid at temperatures below freezing. In some cases, water can remain liquid even at a temperature of -20°C. The reason for this effect is that in order for the first ice crystals to begin to form, crystal formation centers are needed. If they are not present in liquid water, then supercooling will continue until the temperature drops enough that crystals begin to form spontaneously. When they begin to form in the supercooled liquid, they will begin to grow faster, forming slush ice, which will freeze to form ice. Hot water is most susceptible to hypothermia because heating it removes 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 the case of cold water, which is not supercooled, the following happens: a thin layer of ice forms on its surface, which acts as an insulator between water and cold air, and thereby prevents further evaporation. The rate of formation of ice crystals in this case will be lower. In the case of hot water subjected to supercooling, the supercooled 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 forms more ice. 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 heat loss, while hot water begins to freeze from below. This effect is explained by an anomaly in water density. Water has its maximum density at 4°C. If you cool water to 4°C and place it in an environment with a lower temperature, the surface layer of water will freeze faster. Because this water is less dense than water at 4°C, it will remain on the surface, forming a thin cold layer. Under these conditions, a thin layer of ice will form on the surface of the water within a short time, but this layer of ice will act 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 quickly due to evaporation and bigger 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 an equilibrium point? To explain the Mpemba effect from the point of view of convection, it would be necessary 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 the process of convection.
Gases dissolved in water
Water always contains gases dissolved in it - oxygen and carbon dioxide. These gases have the ability to reduce the freezing point of water. When water is heated, these gases are released from the water because their solubility in water is lower at high temperatures. Therefore, when hot water cools, it always contains less dissolved gases 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 is no experimental data confirming this fact.
Thermal conductivity
This mechanism can play a significant role when water is placed in the refrigerator compartment freezer in small containers. Under these conditions, it has been observed that a container of hot water melts the ice in the freezer underneath, thereby improving thermal contact with the freezer wall and thermal conductivity. As a result, heat is removed from a hot water container faster than from a cold one. In turn, a container with cold water does not melt the snow underneath. All these (as well as other) conditions were studied in many experiments, but an unambiguous answer to the question - which of them ensure 100% reproduction of the Mpemba effect - was never obtained. For example, in 1995, German physicist David Auerbach studied the effect of supercooling 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 a supercooled state faster than hot water, thereby compensating for the previous lag. In addition, Auerbach's results contradicted previous data that hot water was able to achieve greater supercooling due to fewer crystallization centers. When water is heated, gases dissolved in it are removed from it, and when it is boiled, some salts dissolved in it precipitate. For now, only one thing can be stated: the reproduction of this effect significantly depends on the conditions under which the experiment is carried out. Precisely because it is not always reproduced.
But as they say, the most likely reason.
As the chemists write in their article, which can be found on the preprint website arXiv.org, hydrogen bonds are stronger in hot water than in cold water. Thus, it turns out that more energy is stored in the hydrogen bonds of hot water, which means that more of it is released when cooled to sub-zero temperatures. For this reason, hardening occurs faster.
To date, scientists have solved this mystery only theoretically. When they present convincing evidence of their version, the question of why hot water freezes faster than cold water can be considered closed.
There are many factors that influence which water freezes faster, hot or cold, but the question itself seems a little strange. The implication, and this is known from physics, is that hot water still needs time to cool to the temperature of the cold water being compared in order to turn into ice. Cold water can skip this stage, and, accordingly, it gains time.
But the answer to the question of which water freezes faster - cold or hot - outside in the cold, any resident of northern latitudes knows. In fact, scientifically, it turns out that in any case, cold water is simply bound to freeze faster.
The physics teacher, to whom schoolboy Erasto Mpemba approached in 1963, thought the same thing with a request to explain why the cold mixture of future ice cream takes longer to freeze than a similar, but hot one.
“This is not universal 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 visited the same school where Erasto studied, experimentally confirmed the presence of such an effect, although there was no explanation for it then. In 1969, a joint article by these two people was published in a popular scientific journal, who described this peculiar effect.
Since then, by the way, the question of which water freezes faster - hot or cold - has proper name- the effect, or paradox, of Mpemba.
The question has been around for a long time
Naturally, such a phenomenon took place before, and it was mentioned in the works of other scientists. Not only the schoolchild was interested in this issue, but Rene Descartes and even Aristotle also thought about it at one time.
But they began to look for approaches to solving this paradox only at the end of the twentieth century.
Conditions for a paradox to occur
As with ice cream, it's not easy plain water freezes during the experiment. Certain conditions must be present in order to start arguing which water freezes faster - cold or hot. What influences the course of 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 as the volume decreases, the freezing time becomes shorter than if we take the same initial volume of cold water.
It's been a while since you defrosted the freezer.
Which water freezes faster and why this happens can be influenced 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 contains hot water and the other cold, the container with hot water will melt the snow underneath, thereby improving the contact of the thermal level with the wall of the refrigerator. A container of cold water cannot do this. If there is no such lining with snow in the refrigerator compartment, 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 begins to freeze at upper layers, when hot it does the opposite - it begins to freeze from the bottom up. It turns out that cold water, having a cold layer on top with ice already formed in places, thus worsens the processes of convection and thermal radiation, thereby explaining which water freezes faster - cold or hot. Photos from amateur experiments are attached, and this is clearly visible here.
The heat goes out, rushing upward, 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 obstacles in its path. Which one freezes faster - cold or hot, what determines the likely outcome? You can expand the answer by saying that any water has certain substances dissolved in it.
Impurities in water as a factor influencing the outcome
If you don’t cheat and use water with the same composition, where are the concentrations? certain substances are identical, then cold water should freeze faster. But if a situation occurs when dissolved chemical elements are available only in hot water, and 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 a solid state is difficult. It is even possible that the water will be supercooled, in the sense that at sub-zero temperatures it will be in a liquid state.
But all these versions, apparently, did not completely suit the scientists and they continued to work on this issue. In 2013, a team of researchers in Singapore said they had solved an age-old mystery.
A group of Chinese scientists claim that the secret of this effect lies in the amount of energy that is stored between water molecules in its bonds, called hydrogen bonds.
The answer from Chinese scientists
What follows is information, to understand which you need to have some knowledge of chemistry in order to understand which water freezes faster - hot or cold. As is known, it consists of two H (hydrogen) atoms and one O (oxygen) atom, held together by covalent bonds.
But also the hydrogen atoms of one molecule are attracted to neighboring molecules, to their oxygen component. These bonds are called hydrogen bonds.
It is worth remembering that at the same time, water molecules have a repulsive effect 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 by occupying the same distance between the molecules in a cold state, they can be said to stretch, and they have a greater supply of energy. It is this energy reserve that is released when water molecules begin to move closer to each other, that is, cooling occurs. It turns out that a greater reserve of energy in hot water, and its greater release when cooling to sub-zero temperatures, occurs faster than in cold water, which has a smaller reserve of such energy. So which water freezes faster - cold or hot? On the street and in the laboratory, Mpemba's paradox should occur, and hot water should turn into ice faster.
But the question is still open
There is only theoretical confirmation of this solution - all this is written in beautiful formulas and seems plausible. But when the experimental data on which water freezes faster - hot or cold - are put into practical use, and their results are presented, then the question of Mpemba’s paradox can be considered closed.
The British Royal Society of Chemistry is offering a £1,000 reward to anyone who can explain scientific point understanding why in some cases hot water freezes faster than cold water.
“Modern science still cannot answer this seemingly simple question. Ice cream makers and bartenders use this effect in their daily work, but no one really knows why it works. This problem has been known for millennia, with philosophers such as Aristotle and Descartes thinking about it,” said Professor David Phillips, president of the British Royal Society of Chemistry, as quoted in a Society press release.
How a cook from Africa defeated a British physics professor
This is not an April Fool's joke, but a harsh physical reality. Modern science, which easily operates with galaxies and black holes, and builds giant accelerators to search for quarks and bosons, cannot explain how elementary water “works.” The school textbook clearly states that it takes more time to cool a hotter body than to cool a cold body. But for water, this law is not always observed. Aristotle drew attention to this paradox in the 4th century BC. e. Here is what the ancient Greek wrote in his book Meteorologica I: “The fact that water is preheated causes it to freeze. Therefore, many people, when they want to cool hot water faster, first place it in the sun...” In the Middle Ages this phenomenon Francis Bacon and Rene Descartes tried to explain. Alas, neither the great philosophers nor the numerous scientists who developed classical thermophysics succeeded in this, and therefore such an inconvenient fact was “forgotten” for a long time.
And only in 1968 they “remembered” thanks to the schoolboy Erasto Mpembe from Tanzania, far from any science. While studying at culinary arts school in 1963, 13-year-old Mpembe was given the task of making ice cream. According to the technology, it was necessary to boil milk, dissolve sugar in it, cool it to room temperature, and then put it in the refrigerator to freeze. Apparently, Mpemba was not a diligent student and hesitated. Fearing that he would not make it by the end of the lesson, he put still hot milk in the refrigerator. To his surprise, it froze even earlier than the milk of his comrades, prepared according to all the rules.
When Mpemba shared his discovery with his physics teacher, he laughed at him in front of the whole class. Mpemba remembered the insult. Five years later, already a student at the university in Dar es Salaam, he attended a lecture by the famous physicist Denis G. Osborne. After the lecture, he asked the scientist a question: “If you take two identical containers with equal amounts of water, one at 35 °C (95 °F) and the other at 100 °C (212 °F), and place them in the freezer, then Water in a hot container will freeze faster. Why?" Can you imagine the reaction of a British professor to a question from a young man from forgotten by God Tanzania. He made fun of the student. However, Mpemba was ready for such an answer and challenged the scientist to a bet. Their dispute ended with an experimental test that confirmed Mpemba was right and Osborne defeated. Thus, the apprentice cook wrote his name in the history of science, and from now on this phenomenon is called the “Mpemba effect.” It is impossible to discard it, to declare it as “non-existent”. The phenomenon exists, and, as the poet wrote, “it doesn’t hurt.”
Are dust particles and solutes to blame?
Over the years, many have tried to unravel the mystery of freezing water. A whole bunch of explanations for this phenomenon have been proposed: evaporation, convection, the influence of dissolved substances - but none of these factors can be considered definitive. A number of scientists have devoted their entire lives to the Mpemba effect. Employee of the Department of Radiation Safety State University New York - James Brownridge - in free time has been studying the paradox for over a decade now. After conducting hundreds of experiments, the scientist claims to have evidence of the “guilt” of hypothermia. Brownridge explains that at 0°C, water only becomes supercooled, and begins to freeze when the temperature drops below. The freezing point is regulated by impurities in the water - they change the rate of formation of ice crystals. Impurities, such as dust particles, bacteria and dissolved salts, have a characteristic nucleation temperature when ice crystals form around crystallization centers. When there are several elements in water at once, the freezing point is determined by the one that has the most high temperature nucleation.
For the experiment, Brownridge took two water samples of the same temperature and placed them in the freezer. He discovered that one of the specimens always froze before the other, presumably due to a different combination of impurities.
Brownridge says hot water cools faster because there is a greater difference between the temperature of the water and the freezer - this helps it reach its freezing point before cold water reaches its natural freezing point, which is at least 5°C lower.
However, Brownridge's reasoning raises many questions. Therefore, those who can explain the Mpemba effect in their own way have a chance to compete for a thousand pounds sterling from the British Royal Society of Chemistry.
Many researchers have put forward and are putting forward their own versions as to why hot water freezes faster than cold water. It would seem like a paradox - after all, in order to freeze, hot water first needs to cool. However, the fact remains a fact, and scientists explain it in different ways.
Major versions
On at the moment There are several versions that explain this fact:
- Because hot water evaporates faster, its volume decreases. And freezing of a smaller amount of water at the same temperature occurs faster.
- The freezer compartment of the refrigerator has a snow liner. A container containing hot water melts the snow underneath. This improves thermal contact with the freezer.
- Freezing of cold water, unlike hot water, begins at the top. At the same time, convection and heat radiation, and, consequently, heat loss worsen.
- Cold water contains crystallization centers - substances dissolved in it. If their content in water is small, icing is difficult, although at the same time, supercooling is possible - when at sub-zero temperatures it has a liquid state.
Although in fairness it can be said that this effect is not always observed. Very often, cold water freezes faster than hot water.
At what temperature does water freeze
Why does water freeze at all? It contains a certain amount of mineral or organic particles. These could be, for example, very small particles of sand, dust or clay. As the air temperature decreases, these particles are the centers around which ice crystals form.
The role of crystallization nuclei can also be played by air bubbles and cracks in the container containing water. The speed of the process of turning water into ice is largely influenced by the number of such centers - if there are many of them, the liquid freezes faster. At normal conditions, with normal atmospheric pressure, water turns into a solid state from liquid at a temperature of 0 degrees.
The essence of the Mpemba effect
The Mpemba effect is a paradox, the essence of which is that under certain circumstances, hot water freezes faster than cold water. This phenomenon was noticed by Aristotle and Descartes. However, it was not until 1963 that Tanzanian schoolboy Erasto Mpemba determined that hot ice cream took longer to freeze. short time than cold. He made this conclusion while completing a cooking assignment.
He had to dissolve sugar in boiled milk and, having cooled it, place it in the refrigerator to freeze. Apparently, Mpemba was not particularly diligent and began completing the first part of the task late. Therefore, he did not wait for the milk to cool down, and put it in the refrigerator hot. He was very surprised when it froze even faster than that of his classmates, who were doing the work in accordance with the given technology.
This fact interested the young man very much, and he began experiments with plain water. In 1969, the journal Physics Education published the results of research by Mpemba and Professor Dennis Osborne of the University of Dar Es Salaam. The effect they described was given the name Mpemba. However, even today there is no clear explanation for the phenomenon. All scientists agree that the main role in this belongs to the differences in the properties of chilled and hot water, but what exactly is unknown.
Singapore version
Physicists from one of the Singapore universities were also interested in the question of which water freezes faster - hot or cold? A team of researchers led by Xi Zhang explained this paradox precisely by the properties of water. Everyone knows the composition of water from school - an oxygen atom and two hydrogen atoms. Oxygen to some extent pulls electrons away from hydrogen, so the molecule is a certain kind of “magnet”.
As a result, certain molecules in water are slightly attracted to each other and are united by a hydrogen bond. Its strength is many times lower than a covalent bond. Singaporean researchers believe that the explanation for Mpemba's paradox lies precisely in hydrogen bonds. If water molecules are placed very tightly together, then such a strong interaction between the molecules can deform the covalent bond in the middle of the molecule itself.
But when water is heated, the bound molecules move slightly away from each other. As a result, relaxation of covalent bonds occurs in the middle of the molecules with the release of excess energy and a transition to a lower energy level. This leads to the fact that hot water begins to cool quickly. At least, this is what theoretical calculations carried out by Singaporean scientists show.
Instantly freezing water - 5 incredible tricks: Video
It would seem that the good old formula H 2 O contains no secrets. But in fact, water - the source of life and the most famous liquid in the world - is fraught with many mysteries that even scientists are sometimes unable to solve.
Here are the 5 most interesting facts about water:
1. Hot water freezes faster than cold water
Let's take two containers with 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 according to the logic of things, cold water should have turned into ice first: after all, hot water must first cool to the cold temperature, and then turn into ice, while cold water does not need to cool. Why is this happening?
In 1963, Erasto B. Mpemba, a high school student in Tanzania, was freezing an ice cream mixture and noticed that the hot mixture solidified faster in the freezer than the cold one. When the young man shared his discovery with his 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 actually freezes faster than cold water.
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 René Descartes.
Scientists still do not fully understand the nature of this phenomenon, explaining it either by the difference in supercooling, evaporation, ice formation, convection, or by the effect of liquefied gases on hot and cold water.
Note from X.RU on the topic “Hot water freezes faster than cold water.”
Since the issues of cooling are closer to us, refrigeration specialists, we will allow ourselves to delve a little deeper into the essence of this problem and give two opinions about the nature of such a mysterious phenomenon.
1. A scientist from the University of Washington has proposed 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, not hot, water into the washer reservoir in winter. But what lies behind this phenomenon? for a long time remained unknown.
Dr. Jonathan Katz from the University of Washington studied this phenomenon and came to the conclusion that substances dissolved in water, which precipitate when heated, play an important role, reports EurekAlert.
Under dissolved substances dr. Katz refers to calcium and magnesium bicarbonates, which are found in hard water. When 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 the water increases 50 times. Because of this, the freezing point of water decreases. “And now the water has to cool further to freeze,” explains Dr. Katz.
There is a second reason that prevents unheated water from freezing. 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 cools down less well,” comments Dr. Katz.
According to the scientist, his theory can be tested experimentally, because The Mpemba effect becomes more noticeable for harder water.
2. Oxygen plus hydrogen plus cold creates ice. At first glance, this transparent substance seems very simple. In reality, ice is fraught with many mysteries. Ice, created by the African Erasto Mpemba, did not think about fame. The days were hot. He wanted fruit ice. He took the juice box and put it in the freezer. He did this more than once and therefore noticed that the juice freezes especially quickly if you first hold it in the sun - it really heats it up! This is strange, thought the Tanzanian schoolboy, who acted contrary to worldly wisdom. Is it really true 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 sixties of the last century. 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 onto the walls of the vessel. "Of course, water with high content the air 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 appears 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 atom. However, ice is perhaps the most mysterious substance in the Universe. Scientists have not yet been able to explain some of its properties.
2. Supercooling and "instant" freezing
Everyone knows that water always turns into ice when cooled 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 cooled to below freezing. This phenomenon becomes possible due to the fact that environment does not contain centers or nuclei of crystallization that could trigger the formation of ice crystals. And so water remains in liquid form even when cooled to below zero degrees Celsius. The crystallization process can be triggered, for example, by gas bubbles, impurities (contaminants), or an uneven surface of the container. Without them, water will remain in a liquid state. When the crystallization process starts, you can watch the super-cooled water instantly turn into ice.
Watch the video (2,901 KB, 60 sec) from 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 various conditions is there near the water?
If you answered three (solid, liquid, gas), then you were wrong. Scientists identify at least 5 different states of liquid water 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-chilled water suddenly turns into ice. What happens with further decline?
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 “vitreous” water - a solid substance that lacks 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 yielded an unexpected result: physicists discovered that neutrons aimed at water molecules “see” 25% fewer hydrogen protons than expected.
It turned out that at a speed of one attosecond (10 -18 seconds) an unusual quantum effect takes place, and the chemical formula of water, instead of the usual one - H 2 O, becomes H 1.5 O!
5. Does water have memory?
Homeopathy, an alternative to conventional medicine, claims that a diluted solution medicinal product can have a healing effect on the body, even if the dilution factor is so high that there is nothing left in the solution except 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 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 group 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 refute this concept once and for all. The result was the opposite. After What, scientists said that they were able to prove the reality of the “water memory” effect. However, experiments conducted under the supervision of independent experts did not bring any results. The debate about the existence of the “water memory” phenomenon continues.
Water has many other unusual properties that we did not talk about 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. Nepomnyashchy N.N. Secrets of inanimate nature. The most mysterious substance in the universe / http://www.bibliotekar.ru.
