Hi, Chris. The Mpemba effect is the theory that warmer water can freeze faster than colder water.
The effect has been noted since ancient times but scientists have struggled to explain why it occurs.
A team of Singapore scientists finally think they have solved the mystery and think the secret lies in the unique properties of the bonds that hold water together.
Hydrogen bonds bring individual water molecules into close contact, which triggers natural repulsion between the water molecules and causes the bonds between oxygen and hydrogen atoms to stretch as well as store energy.
So as the liquid warms, it makes the water molecules sit further apart from each other as the hydrogen bonds stretch.
When the molecules shrink again and give up their energy, this results in it cooling, which the scientists say means that warm water cools faster than cold water and explains the Mpemba effect.
You can read more about new research found at this site:
First, the process of evaporation is endothermic, which means it takes energy for something to evaporate. As a molecule of water evaporates, it leaves the surface of the water and flies into the atmosphere. Thus, in simplified terms, the molecule converted heat energy into kinetic energy (energy of motion). Since the hot water evaporates quicker than the cold water, it loses heat energy quicker than the cold energy.
Second, since some of the hot water evaporates away, there is less water left to have to freeze.