Hot water freezes faster than cold for a wide range of experimental conditions, known as the Mpemba effect. Evaporation is the strongest candidate to explain the Mpemba effect. As hot water placed in an open container begins to cool, the overall mass decreases as some of the water evaporates. With less water to freeze, the process can take less time.

Mpemba effect

This apparent quirk of nature is the "Mpemba effect," named after the Tanzanian high school student, Erasto Mpemba, who first observed it in 1963. The Mpemba effect occurs when two bodies of water with different temperatures are exposed to the same subzero surroundings and the hotter water freezes first. Rene Descartes and Francis Bacon, who also thought that hot water froze faster than cold water.


When you boil water, you're adding energy to water in its liquid state. Because they're so hot, those tiny water droplets start to vaporize. But since cold air can't hold as much water vapor as warmer air, the water condenses. Extremely cold temperatures quickly freeze the water droplets, which fall as ice crystals.

And also hot water makes clear ice because the hot water holds less dissolved air than cold water. Those bubbles in the center of an ice cube come from air dissolved in the water.