Hot water freezes faster than cold water. Which water freezes faster: hot or cold? What does it depend on

Mpemba effect or why does hot water freeze faster than cold water? The Mpemba Effect (Mpemba Paradox) is 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. Erasto Mpemba was a student at Magambin High School in Tanzania doing practical cooking work. He had 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 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 at the Mkvava High School, he asked Professor Dennis Osborne from the University College in Dar es Salaam (invited by the director of the school to give a lecture on physics to the 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 the 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 a few explanations for the Mpemba effect: Evaporation Hot water evaporates faster from a 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 effect of evaporation 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. Subcooling 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 a temperature of -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 the 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 quickly due to evaporation and a greater temperature difference. Also, cold water layers are denser than hot water layers, so the cold water layer will sink down, lifting the warm water layer 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, it would be assumed 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 are no experimental data that would confirm this hypothesis that cold and hot water layers 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 is lower. 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 freezer refrigerator 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

In 1963, a schoolboy from Tanzania named Erasto Mpemba asked his teacher a stupid question - why did warm ice cream freeze faster than cold ice cream in his freezer?

Erasto Mpemba was a student at Magambin High School in Tanzania doing practical cooking work. He had 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 procrastinated on the first part of the assignment. Fearing that he would not be in time 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 a given technology.

He turned to the physics teacher for clarification, but he only laughed at the student, saying the following: "This is not world physics, but the physics of Mpemba." After that, Mpemba experimented not only with milk, but also with ordinary water.

In any case, already being a student at the Mkvava High School, he asked Professor Dennis Osborne from the University College in Dar es Salaam (invited by the director of the school to give a lecture on physics to the 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?" Osborn 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 the Mpemba effect.

Are you curious to know 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 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. 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.

Since then, different versions have been expressed, one of which was as follows: part of the hot water simply evaporates at first, and then, when a smaller amount remains, the water solidifies faster. This version, due to its simplicity, became the most popular, but scientists were not completely satisfied.

Now a team of researchers from the 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 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 - in this case, hydrogen bonds are formed.

At the same time, water molecules as a whole repel each other. Scientists from Singapore noticed that the warmer the water, the greater the distance between the molecules of the liquid due to the 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 approach each other. And the return of energy, as you know, means cooling.

Here are the hypotheses put forward by scientists:

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, due to evaporation, its temperature decreases.

temperature difference

Due to the fact that the temperature difference between hot water and cold air is greater - therefore, heat transfer 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 the case of cold water that is not supercooled, what happens is that a thin layer of ice forms on its surface, which acts as an insulator between the water and the cold air, and thus prevents 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 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 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 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 greater temperature differences. Also, cold water layers are denser than hot water layers, so the cold water layer will sink down, lifting the warm water layer 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 the point of view of convection, it would be assumed 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 water layers 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 is lower. 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 unambiguous 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 a 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, 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 significantly depends on the conditions under which the experiment is carried out. Precisely because it is not always reproduced.

And here's the most likely reason.

As the chemists write in their article, which can be found on the arXiv.org preprint site, hydrogen bonds are stretched more strongly 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, freezing is faster.

To date, scientists have solved this riddle only theoretically. When they present convincing evidence of their version, then the question of why hot water freezes faster than cold water can be considered closed.

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. this stage can be skipped, and, accordingly, she wins in time.

But the answer to the question of which water freezes faster - cold or hot - on the street in frost, any inhabitant of the northern latitudes knows. 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 a popular scientific journal published a joint article by the two men 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. It turns out that cold water, having a cold layer on top with ice already formed in some places, thus worsens the processes of convection 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 dissolved chemical elements are present only in hot water, while cold water does not possess them, then hot water has the opportunity to freeze earlier. This is explained by the fact that the dissolved substances in water create centers of crystallization, and with a small number of these centers, the transformation of water into a solid state is 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 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

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.

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 a paradox - after all, in order to freeze, hot water first needs to cool down. However, the fact remains, and scientists explain it in different ways.

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

1. Since evaporation in hot water is faster, its volume decreases. A smaller amount of water of the same temperature freezes faster.
2. The freezer compartment of the refrigerator has a snow lining. A container containing hot water melts the snow underneath. This improves thermal contact with the freezer.
3. Freezing of cold water, unlike hot, begins from above. In this case, convection and heat radiation, and, consequently, heat loss worsen.
4. In cold water there are centers of crystallization - substances dissolved in it. With a small content of them in water, icing is difficult, although at the same time, its hypothermia is possible - when it has a liquid state at sub-zero temperatures.

Although in fairness it can be said that this effect is not always observed. Cold water often 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, for example, can be very fine particles of sand, dust or clay. As the air temperature drops, these particles become centers around which ice crystals form.

The role of crystallization nuclei can also be performed by air bubbles and cracks in a container containing water. The rate 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 passes into a solid state from liquid at a temperature of 0 degrees.

The essence of the Mpemba effect

The Mpemba effect is understood as 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 Erasto Mpemba, a schoolboy from Tanzania, determined that hot ice cream freezes in a shorter time than cold ice cream. He made such a conclusion while performing the task of cooking.

He had to dissolve sugar in boiled milk and, after cooling it, place it in the refrigerator to freeze. Apparently, Mpemba did not differ in special diligence and began to carry out the first part of the task late. Therefore, he did not wait for the milk to cool, and put it in the refrigerator hot. He was very surprised when it froze even faster than that of his classmates, who did 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 Osborn 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 Singapore's universities were also interested in the question, 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 still knows the composition of water from school - an oxygen atom and two hydrogen atoms. Oxygen to some extent draws electrons 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 the covalent bond. Singaporean researchers believe that the explanation of the Mpemba paradox lies precisely in hydrogen bonds. If water molecules are placed very closely together, then such a strong interaction between 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 return of excess energy and the transition to the lowest energy level. This leads to the fact that hot water begins to cool rapidly. At least, this is what the theoretical calculations carried out by Singaporean scientists show.

Instant Water Freeze - 5 Incredible Tricks: Video

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 thinking and research, I could not draw a logical conclusion. 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 conduct my 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), for 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 than tap water. Despite the previous explanation, some experts argue that boiled water that has cooled to room temperature should freeze faster because the amount of oxygen is reduced as a result of boiling.

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 in this case, we are interested in another question: 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 might be irregular, etc. But whatever 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 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"