Many researchers have put forward and are putting forward their versions as to why hot water freezes faster than cold. 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

At the moment, there are several versions that explain this fact:

1. Because hot water evaporates faster, its volume decreases. And freezing of a smaller amount of water at the same temperature occurs faster.
2. 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.
3. Freezing of cold water, unlike hot water, begins at the top. At the same time, convection and heat radiation, and, consequently, heat loss worsen.
4. 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 we can say 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. Under 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. a 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 else with school days The composition of water is known - 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 that of 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 rapidly. 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 logically, 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 him this unique property of water was noted by Aristotle, Francis Bacon and Rene 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 underlies this phenomenon remained unknown for a long time.

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 whole year conducted an experiment: 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 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 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, states that a diluted solution of a drug can have a healing effect on the body, even if the dilution factor is so great 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.

One of my favorite subjects at school was chemistry. 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 a cold one (with exactly the specified temperature), and place them in an environment with a certain temperature, which one will freeze faster? Of course, the answer immediately suggested itself - a bucket of cold water, but we thought it was 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 thinking and research, I could not come to a logical conclusion. I even decided to skip this lesson that day, so I never learned the solution to this riddle.

Years passed, and I learned many 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 a scientific point of view. And I decided to conduct my own experiment. Since I couldn't find wooden buckets, I used the freezer, stove, some water and a digital thermometer. I will tell you 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), for unknown reasons, proves the opposite: Hot water freezes faster than cold water. One of several explanations is the process of evaporation: if very hot water is placed in a cold environment, 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 than tap water. Despite the previous explanation, some experts argue that boiled water that has cooled to room temperature should freeze faster because boiling reduces the amount of oxygen.

Cold water boils faster than hot water. If hot water freezes faster, then maybe cold water boils faster! This is contrary to common sense and scientists say that this simply cannot be. Hot tap water should actually boil faster than cold water. But using hot water to boil does not save energy. You may use less gas or light, but the water heater will use the same amount of energy needed to heat cold water. (With solar energy the situation is a little different). As a result of heating the water by the water heater, sediment may appear, 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 accordingly lowers the freezing point - which is why some housewives add a little rock salt to their ice cream). But we are in in this case I’m interested in another question: how long will water take to 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 boiling time or temperature.

But here's what I got:

Cold water: I used three 100 ml glass glasses of purified water: one glass with room temperature (72°F/22°C), one with hot water (115°F/46°C), and one with boiled water (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 using a “wooden float”. When the stick placed in the center of the glass no longer touched the base, I considered the water to be 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 findings: Given 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 that had cooled to room temperature. It froze within 60 minutes - still took longer than cold water to freeze.

Boiled water: I took a liter of water at room temperature and put it on the fire. It boiled in 6 minutes. I then cooled it back down to room temperature and added it to it while it was hot. 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 per 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 can hardly be called a laboratory, and perhaps my conclusions contradict reality. My freezer may not freeze food evenly. My glass glasses may have been irregularly shaped, Etc. But no matter what happens in the laboratory, when it comes to freezing or boiling water in the kitchen, the most important thing is common sense. link with interesting facts
about waterall about water

as suggested on the forum.ixbt.com, this effect (the effect of hot water freezing faster than cold water) is called the “Aristotle-Mpemba effect”

Those. Boiled water (chilled) freezes faster than “raw” Water

- a rather simple substance from a chemical point of view, however, it has a number of unusual properties that never cease to amaze scientists. Below are a few facts that few people know about.

1. Which water freezes faster - cold or hot?

In 1963, a Tanzanian student named Erasto B. Mpemba, while freezing an 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 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 “ Mpemba effect" True, long before him this unique property of water was noted by Aristotle, Francis Bacon and Rene 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.

2. It can freeze instantly

Everyone knows that water always turns to ice when cooled to 0°C... with some exceptions! An example of such a case is supercooling, which is the property of very pure water to remain liquid even when cooled to below freezing. This phenomenon is made possible due to the fact that the 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.

Crystallization process can be caused, 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.

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 does water have? If you answered three: solid, liquid, gas, then you were wrong. 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-chilled water will suddenly turn into ice. What will happen 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 “vitreous” or “vitreous” water - a solid substance 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 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 H2O, becomes H1.5O!

5. Water memory

Alternative to official medicine homeopathy states that a dilute solution of a drug can have a therapeutic effect on the body, even if the dilution factor is so great 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 that was 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 of Queen's University of Belfast, who had criticized the principles of homeopathy, conducted an experiment in 2002 to disprove the concept once and for all. The result was the opposite. After which, scientists stated that they were able to prove the reality of the effect “ water memory" However, experiments carried out 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 did not talk about in this article. For example, the density of water changes depending on temperature (the density of ice is less than the density of water); water has a fairly high surface tension; in the liquid state, water is a complex and dynamically changing network of water clusters, and it is the behavior of the 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", authored by Martin Chaplin, professor at the University of London.

In this article we will look at the question of why hot water freezes faster than cold water.

Heated water freezes much faster than cold water! This amazing property of water, for which scientists still cannot find an exact explanation, has been known since ancient times. For example, even in Aristotle there is a description of winter fishing: fishermen inserted fishing rods into holes in the ice, and so that they would freeze faster, they poured warm water on the ice. This phenomenon was named after Erasto Mpemba in the 60s of the 20th century. Mnemba noticed a strange effect while making ice cream and turned to his physics teacher, Dr. Denis Osborne, for an explanation. Mpemba and Dr. Osborne experimented with water at different temperatures and concluded that almost boiling water begins to freeze much faster than water at room temperature. Other scientists conducted their own experiments and each time obtained similar results.

Explanation of a physical phenomenon

There is no generally accepted explanation for why this happens. Many researchers suggest that the whole point is in the supercooling of the liquid, which occurs when its temperature drops below the freezing point. In other words, if water freezes at a temperature below 0°C, then supercooled water can have a temperature of, for example, -2°C and still remain liquid without turning into ice. When we try to freeze cold water, there is a chance that it will first become supercooled and only harden after some time. Other processes occur in heated water. Its faster transformation into ice is associated with convection.

Convection- this is a physical phenomenon in which the warm lower layers of a liquid rise, and the upper, cooled ones, fall.