Which water hardens faster hot or cold. Why does hot water freeze faster than cold water? Mpemba effect
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.
As a student of the Magamba high school in Tanzania, Erasto Mpemba did practical work in the culinary arts. He had to make homemade ice cream - boil milk, dissolve sugar in it, cool it to room temperature and then place in the refrigerator to freeze. Apparently, Mpemba was not a particularly diligent student and procrastinated on the first part of the assignment. Fearing that he would not be in time by the end of the lesson, he put the still hot milk in the refrigerator. To his surprise, it froze even earlier than the milk of his comrades, prepared according to a given technology.
After that, Mpemba experimented not only with milk, but also with plain water. In any case, already being a student at 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 students) about water: "If you take two identical containers with equal volumes of water so that in one of them the water has a temperature of 35 ° C, and in the other - 100 ° C, and put them in the freezer, then in the second the water will freeze faster. Why? Osborne became interested in this issue and soon in 1969, together with Mpemba, they published the results of their experiments in the journal "Physics Education". Since then, the effect they discovered is called Mpemba effect.
Until now, no one knows exactly how to explain this strange effect. Scientists do not have a single version, although there are many. It's all about the difference in the properties of hot and cold water, but it is not yet clear which properties play a role in this case: the difference in supercooling, evaporation, ice formation, convection, or the effect of liquefied gases on water during different temperatures.
The paradox of the Mpemba effect is that the time during which the body cools down to the ambient temperature must be proportional to the temperature difference between this body and the environment. This law was established by Newton and since then has been confirmed many times in practice. In the same effect, water at 100°C cools down to 0°C faster than the same amount of water at 35°C.
However, this does not yet imply a paradox, since the Mpemba effect can also be explained within known physics. Here are some explanations for the Mpemba effect:
Evaporation
Hot water evaporates faster from the container, thereby reducing its volume, and a smaller volume of water with the same temperature freezes faster. Water heated to 100 C loses 16% of its mass when cooled to 0 C.
The evaporation effect is a double effect. First, the mass of water required for cooling is reduced. And secondly, the temperature decreases due to the fact that the heat of evaporation of the transition from the water phase to the vapor phase decreases.
temperature difference
Because the temperature difference between hot water and more cold air - hence the heat exchange in this case is more intense and hot water cools faster.
hypothermia
When water is cooled below 0 C, it does not always freeze. Under certain conditions, it can undergo supercooling while continuing to remain liquid at temperatures below the freezing point. In some cases, water can remain liquid even at -20 C.
The reason for this effect is that in order for the first ice crystals to begin to form, centers of crystal formation are needed. If they are not in liquid water, then supercooling will continue until the temperature drops enough that crystals begin to form spontaneously. When they start to form in the supercooled liquid, they will start to grow faster, forming an ice slush that will freeze to form ice.
Hot water is most susceptible to hypothermia because heating it eliminates dissolved gases and bubbles, which in turn can serve as centers for the formation of ice crystals.
Why does hypothermia cause hot water to freeze faster? In case of cold water, which is not supercooled, the following occurs. In this case, a thin layer of ice will form on the surface of the vessel. This layer of ice will act as an insulator between the water and cold air and will prevent further evaporation. The rate of formation of ice crystals in this case will be less. In the case of hot water undergoing subcooling, the subcooled water does not have a protective surface layer of ice. Therefore, it loses heat much faster through the open top.
When the supercooling process ends and the water freezes, much more heat is lost and therefore more ice.
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. In addition, cold layers of water are denser than layers hot water, so the layer of cold water will sink down, raising the layer warm water to the surface. This circulation of water ensures a rapid drop in temperature.
But why does this process not reach the equilibrium point? To explain the Mpemba effect from this point of view of convection, one would have to assume that the cold and hot layers of water are separated and the convection process itself continues after the average water temperature drops below 4 C.
However, there is no experimental evidence to support this hypothesis that cold and hot layers of water are separated by convection.
gases dissolved in water
Water always contains gases dissolved in it - oxygen and carbon dioxide. These gases have the ability to lower the freezing point of water. When the water is heated, these gases are released from the water because their solubility in water at high temperature 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 the freezer. refrigerator compartment 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.
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 Mkwawa 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 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 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.
Water- a fairly simple substance from a chemical point of view, however, it has a number of unusual properties that never cease to amaze scientists. Below are some facts that few people know about.
1. Which water freezes faster - cold or hot?
Take two containers of water: pour hot water into one and cold water into the other, and place them in the freezer. Hot water will freeze faster than cold water, although logically, cold water should have turned into ice first: after all, hot water must first cool down to cold temperature, and then turn into ice, while cold water does not need to cool down. Why is this happening?
In 1963, a Tanzanian student named Erasto B. Mpemba, while freezing a prepared ice cream mixture, noticed that the hot mixture solidified faster in the freezer than the cold one. When the young man shared his discovery with a physics teacher, he only laughed at him. Fortunately, the student was persistent and persuaded the teacher to conduct an experiment, which confirmed his discovery: in 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 it unique property water was noted by Aristotle, Francis Bacon and Rene Descartes.
Scientists do not fully understand the nature of this phenomenon, explaining it either by the difference in hypothermia, evaporation, ice formation, convection, or the effect of liquefied gases on hot and cold water.
2. She is able to freeze instantly
Everyone knows that water always turns to ice when cooled to 0 °C ... except in some cases! Such a case, for example, is supercooling, which is a property of very clean water remain liquid even when chilled below freezing. This phenomenon is made possible by the fact that environment does not contain centers or nuclei of crystallization, which could provoke the formation of ice crystals. And so water remains in liquid form, even when cooled to temperatures below zero degrees Celsius.
crystallization process can be provoked, for example, by gas bubbles, impurities (contaminants), uneven surface containers. Without them, the water will remain in liquid state. When the crystallization process starts, you can watch how the super-cooled water instantly turns into ice.
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 the water have? If you answered three: solid, liquid, gaseous, then you are mistaken. Scientists distinguish at least 5 different states of water in liquid form and 14 states in frozen form.
Remember the conversation about super-cooled water? So, no matter what you do, at -38 ° C, even the purest super-cooled water will suddenly turn into ice. What happens as the temperature drops further? At -120°C, something strange begins to happen to water: it becomes super-viscous or viscous, like molasses, and at temperatures below -135°C, it turns into "glassy" or "glassy" water - a solid that lacks crystalline structure.
4. Water surprises physicists
At the molecular level, water is even more surprising. In 1995, a neutron scattering experiment conducted by scientists gave an unexpected result: physicists found that neutrons directed at water molecules “see” 25% fewer hydrogen protons than expected.
It turned out that at the speed of one attosecond (10 -18 seconds) an unusual quantum effect takes place, and chemical formula water instead H2O, becomes H1.5O!
5. Water memory
Alternative to official medicine homeopathy states that a dilute solution medicinal product can provide healing effect on the organism, even if the dilution factor is so great that there is nothing left in the solution but water molecules. Proponents of homeopathy explain this paradox with a concept called " water memory”, according to which water at the molecular level has a “memory” of a substance once dissolved in it and retains the properties of a solution of the initial concentration after not a single ingredient molecule remains in it.
An international team of scientists led by Professor Madeleine Ennis of Queen's University of Belfast, who criticized the principles of homeopathy, conducted an experiment in 2002 to disprove the concept once and for all. The result was the opposite. After that, scientists said that they managed to prove the reality of the effect " water memory". However, experiments conducted under the supervision of independent experts did not bring results. Disputes about the existence of the phenomenon " water memory» continue.
Water has many other unusual properties that we have not covered in this article. For example, the density of water varies with temperature (the density of ice is less than that of water); water has quite big size surface tension; in a liquid state, water is a complex and dynamically changing network of water clusters, and it is the behavior of clusters that affects the structure of water, etc.
About these and many other unexpected features water can be read in the article Anomalous properties of water”, the author of which is Martin Chaplin, professor at the University of London.
The British Royal Society of Chemistry is offering a £1,000 reward to anyone who can scientifically explain 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, philosophers such as Aristotle and Descartes have thought about it,” said Professor David Philips, president of the British Royal Society of Chemistry, quoted in a press release from the Society.
How an African chef beat a British physics professor
This is not an April Fool's joke, but a harsh physical reality. Today's 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 unambiguously states that it takes more time to cool a hot 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 the book "Meteorologica I": "The fact that the water is preheated contributes to its freezing. Therefore, many people, when they want to quickly cool hot water, first put it in the sun ... ”In the Middle Ages, Francis Bacon and Rene Descartes tried to explain this phenomenon. Alas, neither the great philosophers nor the numerous scientists who developed classical thermal physics 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 Mpemba from Tanzania, far from any science. While studying at a cooking 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 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 all the rules.
When Mpemba shared his discovery with a physics teacher, he made fun of him in front of the whole class. Mpemba remembered the insult. Five years later, already a student at the University of Dar es Salaam, he was at 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 the same amount of water, one at 35 °C (95 °F) and the other at 100 °C (212 °F), and put 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 forgotten by God Tanzania. He made fun of the student. However, Mpemba was ready for such an answer and challenged the scientist to a wager. Their argument culminated in an experimental test that proved Mpemba right and Osborne defeated. So the student-cooker inscribed his name in the history of science, and henceforth this phenomenon is called the "Mpemba effect". To discard it, to declare it as if "non-existent" does not work. The phenomenon exists, and, as the poet wrote, "not in the tooth with a foot."
Are dust particles and dissolved substances 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 solutes - but none of these factors can be considered definitive. A number of scientists 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 that he has evidence of the "guilt" of hypothermia. Brownridge explains that at 0°C, water only supercools, 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, and these are dust particles, bacteria and dissolved salts, have their characteristic nucleation temperature, when ice crystals form around the crystallization centers. When several elements are in the water at once, the freezing point is determined by the one that has the most high temperature nucleation.
For the experiment, Brownridge took two samples of water at the same temperature and placed them in a freezer. He found that one of the specimens always freezes before the other - presumably due to different combination impurities.
Brownridge claims that hot water cools faster due to the greater temperature difference between 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.
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 household myths about the boiling point and freezing point of water, and one myth said: "hot water freezes faster." I looked at many websites but the information was too conflicting. And these were just opinions, unfounded from the point of view of science. And I decided to take own experience. Since I couldn't find wooden buckets, I used a freezer, stovetop, some water, and a digital thermometer. I will talk about the results of my experience a little later. First, I will share with you some interesting arguments about water:
Hot water freezes faster than cold water. Most experts say that cold water will freeze faster than hot water. But one funny phenomenon (the so-called Memba effect), 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 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. (WITH solar energy things are a bit different). As a result of heating the water with a water heater, sediment may form, so the water will take longer to heat up.
If you add salt to water, it will boil faster. Salt increases the boiling point (and therefore lowers the freezing point - which is why some housewives add a little rock salt to ice cream). But us in this case another question is of interest: how long will the water boil and whether the boiling point in this case can rise above 100 ° C). Despite what cookbooks say, scientists say that the amount of salt we add to boiling water is not enough to affect the time or temperature of the boil.
But here's what I got:
Cold water: I used three 100 ml glass beakers of purified water: one glass at 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 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 to conduct such experience with earlier boiled water cooled down 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 foods unevenly. My glass glasses could be irregular shape, Etc. But whatever happens in the laboratory, when we are talking about freezing or boiling water in the kitchen, the most important thing is common sense.
link from interesting facts about waterall about water
as suggested on the forum.ixbt.com forum, this effect (the effect of freezing hot water faster than cold water) is called the "Aristotle-Mpemba effect"
Those. boiled water (chilled) freezes faster than "raw"
