Hot water freezes faster than cold water…honest!
Recently, The Royal Society of Chemistry opened a competition for scientists to prove this phenomenon, known as the Mpemba effect.
This observation was first discovered in 400AD by Aristotle, then later Francais Beacon and Rene Descartes, all of who couldn’t put their finger on the explanation.
The effect was catapulted back into the lime light in 1963, by Mpemba a Tanzanian student, who noticed his hot ice cream mix froze quicker than the cold mix.
Numerous theories were thrown around which included: faster evaporation of hot water causing a reduction in the volume left to freeze and different solute concentrations like carbon dioxide. Mpemba’s findings were published, which led to a team of physicists in Singapore to gather evidence showing that the water’s chemical bonds causes this effect.
One water molecule is formulated by the covalent binding of one oxygen atom to two hydrogen molecules. These sharing and caring molecules distribute the electrons allowing each water molecule to bind to another via weaker forces known as hydrogen bonds.
Researchers suggest that this interaction causes the phenomenon. As the molecules attract to each other, they would initially repel causing pressure on the covalent bonds and consequently they would store energy. Hotter water had more pressure on these bonds causing the hydrogen bonds to stretch further.
This slinky like mechanism, stretching and shrinking, of the bonds uses up the energy. This energy usage occurs when the water is cooling- so hotter water does cool faster!