On what water freezes faster, hot orcold, affects a lot of factors, 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 can be skipped this stage, and, accordingly, it wins in time.
The same thought occurred to the teacher of physics, 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.
At that time, the teacher just laughed at it, butDenis 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 this at that time. In 1969 in a popular scientific journal came out a joint article of these two people who described this peculiar effect.
Naturally, even earlier this phenomenon hada place to be, 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.
As in the case of ice cream, not just ordinarythe 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,which can explain the given paradox. The fact that the water freezes faster, hot or cold, may depend on the fact that hot water has a higher evaporation rate than the cold. Thus, its volume decreases, and with a decrease in volume and the freezing time becomes less than if we take a similar initial volume of cold water.
On what kind of water freezes faster, and why is ithappens, the snow lining can affect, 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.
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. In this case, it turns out that cold water, having a cold layer on top with already formed ice, worsens convection and thermal 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 thereoccurs with 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.
If you do not cheat and use water withthe 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 there is a possibility for hot water to freeze earlier. 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 riddle.
Further information will follow, for whichIt is necessary to have some knowledge in chemistry to figure out 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 timewater 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 minus 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.
There is only theoretical confirmationThis clue - all this is written beautiful formulas and it seems plausible. But when the experiments data, 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.
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