Hot water can freeze faster than cold- Mpemba effect
Hot water turns to ice faster than cold water. And in the language of science, the name of this matter is the Mpemba effect. It is named after a Tanzanian student who observed in 1963 that a mixture of hot and cold ice cream freezes faster than cold ice cream. This phenomenon was first observed by the great sage Aristotle in the fourth century BC.
Francis Bacon and René Descartes later mentioned the matter. Mpemba published a research paper in 1969 based on his observations. There are several theories about the Mpemba effect. For example,
- (1) Hot water evaporates quickly, shrinks in volume, and freezes;
- (2) Ice particles accumulate on cold water, isolating it from its surroundings;
- (3) When heating water, some of the carbon dioxide in the surrounding air moves away.
However, the same thing does not always happen. Many times the opposite happens—that is, cold water freezes faster than hot water! So why does naturally hot water freeze faster than cold water? So far, no one has been able to find the perfect solution, which is not surprising.
The experiment was led by physicist Ji Zheng and his team at Nanyang Technological University in Singapore. They see that the main reason for the Mpemba effect is the chemical bonding of water. An oxygen atom in a molecule of water is covalently bound to two hydrogen atoms. Water molecules are again bound to each other by weak hydrogen bonds.
According to the research team, the main reason for the Mpemba effect is the different chemical bonds in the water. They say that when water molecules are brought very close to each other, a kind of repulsion naturally occurs between the water molecules. As a result, the covalent bonds between the atoms of water molecules become somewhat tighter and store energy.
When liquid water is heated, the hydrogen bonds in the water begin to spread more, the water density decreases, and the water molecules begin to separate and spread. As the hydrogen bonds of the water molecules tighten, the covalent bonds in the water atoms begin to loosen and contract somewhat.
As a result, the energy stored in them starts to be released. And this process of energy emission is basically the same as the process of cooling of matter. This proves the theory that hot water cools faster than cold water. Researchers have mathematically shown that loosening of covalent bonds in water occurs less often in hot water than in cold water, which is why hot water condenses faster than cold water.
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