It has been observed that the hot water freezes far quicker than the cold water; this is popularly known as the Mpemba effect. This was first noticed by a Tanzanian student in the year 1963; he had observed how the hot ice cream mix froze faster than the cold one. It then struck his mind and he conducted an experiment, which turned out to be successful and proved the entire theory. This finding was so important and impressive that the effect was named after the student.
But this wasn’t the first time when someone had noticed this; it was first noticed in the 4th century BC by Aristotle. It was also noticed by Francis Bacon and Rene Descartes. However, Mpemba was the only observer, who published his research and conclusion in the year 1969.
He included the concept of hot water’s feature of being quickly evaporated and mixed into the air. The volume left to freeze is decreased due to this evaporation. On the other hand, there is a thin frost layer on cold water as well as a lot of concentrations of carbon dioxide and other such solutes.
Even though Mpemba’s theory had proven to be true, no evidences were found for the same.
Recently, Nanyang Technological University in Singapore’s physicists came together. Xi Zhang worked as the leader of this team to find out evidence to prove the Mpemba theory. The team found out that there are chemical bonds in hot water, which allow it to get frozen faster than the cold water. Every single molecule of water has one atom of oxygen bonded with two molecules of hydrogen.
It is the hydrogen bonds, which stretch to relax. When the hold water is frozen, these bonds shrink, which makes them give up on their energies.