True: Hot water can, and frequently does, freeze faster than colder water.
This phenomenon has been discussed for centuries; although, it wasn’t until 1969 that a Tanzanian high school student introduced it to the scientific community. For his troubles, the phenomenon was named the “Mpemba Effect” after the student.
Why Does Warm Water Freeze faster Than Cold Water?
Since then, physicists have verified that hot water often freezes more quickly than cold water. Scientists have not yet been able to definitively explain why this happens, but a few phenomena are thought to contribute:
Evaporation – Hot water evaporates faster than cold water and brings away steam (water), thereby reducing the amount of liquid to be cooled. Less ice is created, but it is made at a faster rate.
Convection – As the hot water cools, its temperature doesn’t stay uniform throughout. The swirling around of the hotter and cooler sections may contribute to faster cooling.
Dissolved Gases – Hot water holds fewer amounts of dissolved gases than cold water. These gases may prevent convection or change the temperature necessary to freeze the liquid.
Container and Surroundings – The container in which the water is held, as well as the surface or the surroundings in which it is placed, may also affect the cooling process differently at different temperatures.
Interesting fact: Ice cream makers use warm milk to take advantage of the Mpemba effect.