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. With cold water, this stage can be skipped, and, accordingly, it wins in time.
But the answer to the question of which water freezes faster - cold or hot - on the street in frost, any 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 the future ice cream freezes longer than the same, but hot.
This is not world physics, but some kind of Mpemba physics
At that time, the teacher only laughed at this, but Deniss Osborn, 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 arose a long time ago
Naturally, such a phenomenon has taken place before, and it was mentioned in the works of other scientists. Not only a schoolboy was interested in this issue, but Francis Bacon, Rene Descartes and even Aristotle thought about it at one time.
That's just the 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 explainthis paradox. Which water freezes faster, hot or cold, may depend on the fact that hot water 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 you take a similar initial volume of cold water.
The freezer has been defrosted for a long time
Which water freezes faster, and why it does, can be affected by the snow lining that might be 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 under it, 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 compartment, cold water should freeze faster.
Top - bottom
Also, the phenomenon of which water freezes faster - hot or cold, is explained as follows. Following certain laws, cold water 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. Photos from amateurexperiments are attached, and this is clearly visible here.
Heat comes out, tending upwards, and there it meets a very chilled 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 likely 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 affecting 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 fully suit the scientists 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 stored between water molecules in its bonds, called hydrogen bonds.
Clue from Chinese scientists
The following information will follow, for the understanding of which you need to have some knowledge in chemistry in order to figure out which water freezes faster - hot or cold. As you know, a water molecule 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. It is these bonds that are called hydrogen bonds.
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 hydrogen bonds, occupying one distance between molecules in a cold state, can be said to be stretched, and they have a larger 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 such a supply.less energy. So which water freezes faster - cold or hot? The Mpemba paradox should be happening outside and in the lab, and hot water should turn to ice faster.
But 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.
