Surely you have seen videos posted on the Internet, where some people were holding a hot water pitcher to boil water in the sky between -40 or -50 degrees Celsius. Notably, this amount of boiling water. froze in an instant, forming a beautiful ice arc in midair. Many people who have finished watching these videos have asked questions: Why is the temperature of boiling water hot to nearly 100 degrees frozen immediately when it falls to the ground?
In a temperature of -40 or -50 degrees Celsius, boiling water freezes in an instant when it is thrown into the sky. Source: NickSchrader
According to scientists, the phenomenon of boiling water freezes before it falls to the ground under low temperature conditions called the Mpemba effect.
Mpemba is a strange phenomenon in which under certain (sometimes occurring) conditions – when co-cooled, hot water can freeze faster than cold water. Interestingly enough, the effect itself is named after Tanzanian high school student Erasto B. Mpemba.
Mpemba first caught sight of this phenomenon in 1963 in a cooking class at Magamba Middle School, when he cooled a hot blend of ice cream (the mix to make ice cream – it was still hot before putting it in the refrigerator). and notice that it hardens faster than the cold blend ice cream.
After graduating, Mpemba transferred to Mkwawa School, Iringa Province, Tanzania. Once, the principal of this school invited Dr. Denis G. Osborne from the university in the city of Dar Es Salaam to lecture on physics.
At the end of the lecture, Erasto Mpemba asked the Doctor a question: “If we have 2 equal cups of water, one 35 ° C cold water and one 100 ° C hot water, together put both cups in the cupboard. ice, the hot water cup will freeze first – Then why?
At that time, this question was full of interesting Mpemba and received only mockery from her classmates, and also from the teacher. However, Dr. Denis G. Osborne subsequently re-experimented the discovery in his workplace, and confirmed Mpemba’s findings. Both teachers and students announced their results in 1969.
Worth mentioning, this strange phenomenon has puzzled the scientific community for many years, when many researchers have come up with different theories to explain the Mpemba effect.
Why does boiling water that is almost 100 degrees hot instantly freeze when it falls to the ground?
In 2017, a study published by researchers at Southern Methodist University (USA) and Nanjing University (China) gave an explanation to clarify this phenomenon more.
Basically, water is made up of two hydrogen atoms and one oxygen atom. Hydrogen bonds, which are formed between the hydrogen atoms and the oxygen atoms of neighboring water molecules, are key to the Mpemba effect.
In cold water, both strong and weak hydrogen bonds are found. Meanwhile, hot water mainly contains only strong hydrogen bonds, since weak hydrogen bonds are broken during heating. According to researchers at Southern Methodist University) and Nanjing University, the broken molecules can form “Hexagonal lattice of ice” and this is the pivotal point of the Mpemba effect.
With cold water alone, the hydrogen bonds still need to be broken for the freezing process to begin. But because the bonds are already broken in hot water, the rock can form more quickly because the structures needed for it already exist.
Earlier, in 2013, a group of physicists at the Nanyang Technological University in Singapore also published research that they believe could further clarify the Mpemba effect.
According to Nanyang University scientists, the key lies in the unusual interactions between hydrogen molecules (water). These molecules are bound together by highly charged bonds, called “hydrogen bonds,” which create tension on the surface of the water and cause it to reach boiling point faster than other liquids. When water molecules shrink again and give off energy, cooling, which means hot water freezes faster than cold water. This helps to explain more about the “Mpemba effect”.
In 2010, scientist James Bulangliqi of State University, New York, USA offered another explanation. According to James Bulangliqi, impurities in water are the key factor that causes hot water to freeze faster.
Specifically, the Mpemba effect comes from an unstable supercool (overcooling). Basically, the water does not freeze when the temperature reaches 0 degrees Celsius. Usually, the water starts to freeze at a lower temperature, ie supercool. The freezing point is decided by impurities, forming the relationship between water and ice.
Under normal circumstances, the water can have several types of impurities, which include dust, dissolved salts and bacteria. Each impurity can affect the freezing mechanism under a special temperature. According to James Bulangliqi, if the freezing point of hot water is at least 5 degrees C high, its freezing rate will be much faster than cold water.
James Bulangliqi also said that if the freezing point of hot water is at least 5 ° C high, its freezing rate will be much faster than cold water.