Is it true that hot water freezes faster that cold water?

Yes http://math.ucr.edu/home/baez/physics/General/hot_...

The phenomenon you describe is one of modern science's few remaining mysteries and the source of much debate in certain circles. Given the right set of conditions, hot or warm water can freeze faster than cooler water.

This strange phenomenon was described by the likes of Aristotle, Bacon, and Descartes, yet is named after the Tanzanian high-school student who demonstrated it in 1969. The Mpemba effect only occurs under very specific sets of conditions and is still not completely understood.

Though the effect has been reproduced successfully in a number of experiments, no one can say with certainty why it happens due to the great number of variables involved. However, it is generally believed some combination of factors, such as evaporation, convection, conduction, and supercooling, may account for the Mpemba effect.

You'll be glad to know that however mysterious the phenomenon is, the Mpemba effect is put to good use by many ice-cream makers, who use warm milk instead of cool to help their ice cream freeze more quickly.

You may also be interested to know that for such a seemingly simple substance, water is surprisingly complex, and its behavior is poorly understood. The Mpemba effect is just one of 38 anomalies of H2O.

yes. thats true. this is called Mpemba effect. because there are lots of factors: evaporation-the temperature drops due to heat lost in causing the phase change from water to vapour (latent heat of evaporation)., supercooling- consider the water which started colder and which does not get supercooled. In this case a thin layer of ice is likely to form quickly on the surface., convection- can continue after the average temperature had dropped below 4C.,dissolved gases-oxygen and carbon dioxide have the effect of lowering its freezing point, and conduction-heat is drawn out of the warmer container more rapidly.

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"Thank you very much" gave a fantastic answer. All I can add is that warmer water has less dissolved oxygen than cold water. It may have an effect.

Doesn't make sense, it would seem cold water would always have a head start, but maybe in some strange phenomenon.

put a ice bar to the hot water