Mpemba Effect

This phenomenon of hot water freezing faster than cold water is known as the Mpemba effect.

I tried this 3 times with the same results.

Hot water seems to freeze faster than cold water, known as the Mpemba effect. The effect was named after the Tanzanian student who in 1963 noticed that hot ice cream mix freezes faster than a cold one. The effect was first observed by Aristotle in the 4th century BC, then later Francis Bacon and René Descartes.

Theories for the Mpemba effect have included faster evaporation of hot water, therefore reducing the volume left to freeze; formation of a frost layer on cold water, insulating it; and different concentrations of solutes such as carbon dioxide, which is driven off when the water is heated. Unfortunately the effect doesn’t always appear – cold water often does actually freeze faster than hot, as you would expect. But this Mpemba effect occurs regularly, and no one has ever been able to definitively answer why.

Here are some of the ideas why hot water freezes faster!

The hot water loses more water molecules through evaporation, so there’s less of it to freeze.

There are more dissolved gasses in cold water than warm water, and researchers have predicted that this could play a role in cooling rates, although it’s not clear how.

The idea that warm water might cool faster due to increased convection currents.

I find it weird that after all these observations, we still have so much to learn about something as basic as freezing water. This is why Science is awesome!