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

The fact that the water freezes faster, hot or cold, many factors affect, but the question itself seems a bit strange. It is implied, and it is known from physics, that hot water still needs time to cool to the temperature of cold water being compared to turn into ice. Cold water, this stage can be skipped, and, accordingly, it wins in time. But any resident of northern latitudes knows the answer to the question of which water freezes faster-cold or hot-outside in the cold. In fact, scientifically, it turns out that in any case, cold water simply must freeze faster.

The same thought occurred to the physics teacher, who was asked by the student Erasto Mpemba in 1963 to explain why the cold mixture of the future ice cream freezes longer than the similar but hot one.

"This is not world physics, but some kind of physics Mpemba"

At that time the teacher only laughed at this, but Denis Osborn, a physics professor who once visited the same school where Erasto studied, experimentally confirmed the existence of such an effect, although there was no explanation for it at that time. In 1969 in a popular scientific journal came out a joint article of these two people who described this peculiar effect. Since then, by the way, the question of which water freezes faster - hot or cold, has its own name - effect, or paradox, Mpemba.

The question arose a long time ago

Naturally, this phenomenon used to exist before, and it was mentioned in the works of other scientists. Not only the student was interested in this matter, but also Francis Bacon, Rene Descartes and even Aristotle thought about this. Only approaches to the solution of this paradox began to look only at the end of the twentieth century.

Conditions for a paradox to occur

As in the case of ice cream, not just ordinary water freezes during the experiment. There must be certain conditions to begin to argue, which water freezes faster - cold or hot. What influences the course of this process?

Now, in the 21st century, several options have been put forward that can explain the danian paradox. The fact that the water freezes faster, hot or cold, may depend on the fact that hot water has a greater evaporation rate than the cold. Thus, its volume decreases, and with a decrease in volume and the freezing time becomes less than if you take a similar initial volume of cold water.

For a long time the freezer was defrosted

The fact that the water freezes faster, and why this happens, can affect the snow lining, which can take place in the freezer of the refrigerator used for the experiment. If you take two containers that are identical in volume, but in one of them there will be hot water and in the other - a cold one, the container with hot water will melt the snow underneath, thereby improving the contact of the heat level with the wall of the refrigerator. A container with cold water can not do this. If there is no 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 begins to freeze from the upper layers, when hot it does the opposite - it starts to freeze from the bottom up. It turns out that cold water, having a cold layer on top with already formed ice, worsens convection and heat radiation, thus explaining which water freezes faster-cold or hot. Photos from amateur experiments are attached, and here it is clearly visible.

Heat comes out, tending upwards, and there it meets a very cooled layer. There is no free path for heat radiation, so the cooling process becomes difficult. Such obstacles in its path absolutely does not have hot water. 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 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 there is a situation when dissolved chemical elements are available only in hot water, and cold water does not have them at that, then it is possible to freeze before hot water. This is explained by the fact that dissolved substances in water create centers of crystallization, and with a small number of these centers, the transformation of water in the solid state is difficult. It is even possible to subcool the water, in the sense that at minus temperature it will be in a liquid state.

But all these versions, apparently, did not fully satisfy the scientists and they continued to work on this issue. In 2013, a team of researchers in Singapore said that they managed to solve an age-old mystery. A group of Chinese scientists argue that the secret of this effect is the amount of energy that is stored between the water molecules in its bonds, called hydrogen ones.

The solution from Chinese scientists

Then follows the information, for understanding which it is necessary to have some knowledge in chemistry in order to understand which water freezes faster - hot or cold. As is known, the water molecule consists of two atoms H (hydrogen) and one atom O (oxygen), held together by covalent bonds.

But also the hydrogen atoms of one molecule are attracted to neighboring molecules, to their oxygen component. It is these connections that are called hydrogen bonds.

It should be remembered that at the same time, water molecules act on each other repulsive. Scientists noted that when water is heated between its molecules, the distance increases, and this is facilitated by just repulsive forces. It turns out that hydrogen bonds, occupying one distance between molecules in the cold state, can be said to stretch, and they have a greater supply of energy. It is this energy reserve that is released when water molecules begin to approach each other, that is, cooling occurs. It turns out that a greater supply of energy in hot water, and its greater release when cooled to sub-zero temperatures, occurs faster than in cold water, which has less energy. So which water freezes faster - cold or hot? On the street and in the laboratory, the Mpemba paradox must occur, and hot water must turn into ice faster.

But the question is still open

There is only theoretical confirmation of this clue - all this is written beautiful formulas and it seems plausible. But when the data of experiments, which water freezes faster - hot or cold, will be put in a practical sense, and their results will be presented, then the question of the Membba paradox can be considered closed.