Why does hot water freeze faster than cold water?

If you have nothing better to think about today, how about trying to solve this old scientific puzzle?

“Why does hot water freeze faster than cold water?”

There is a £1000 pound prize for the best answer:

It seems a simple enough question – yet it has baffled natural philosphers for at least 2,300 years.
  • Aristotle agonized over it fruitlessly in the fourth century BC
  • Descartes was defeated by it in the 17th century AD
  • Even perplexed 20th and 21st century scientists and intellectuals have swarmed over it without result
Now the Royal Society of Chemistry is offering £1000 to the person or team producing the best and most creative explanation of the phenomenon, known today as The Mpemba Effect.


Why does hot water freeze faster than cold water? — 3 Comments

  1. In the third grade our science teacher brought water to a boil then set the teakettle on the palm of his hand for a short time without burning his hand. He had volunteers do the same. I volunteered. At first the bottom of the teakettle just felt warm but quickly turned hot. For some reason the boiling water drew the heat out of the copper coated steel bottom of the teakettle as long as the water kept boiling.

    Just this past Christmas while watching TV I watched a lady who lived in the northern part of Japan trim her outside Christmas tree with snow by throwing boiling water into the air. The boiling water quickly turned to snow and settled on the tree branches. And that doesn’t happen with plain water.

    On hiking and camping trips at altitude, say in the Rockies, it is difficult to cook food in water without a pressure cooker.

    I don’t know if these observations are related in some manner to the subject of hot water freezing faster than cold water. Water has gaseous properties when boiling; therefore it freezes faster–perhaps.

    Dave Fisher

  2. Dave,

    Your comment about water having gaseous properties when boiling; therefore it freezes faster was interesting. There may be something to that. Why don’t you submit your idea to the Royal Society of Chemistry. Maybe you’ll be the £1000 winner!


  3. 原因只在于:水在不同温度时的结构组成不同。大家都知道水结冰时体积是膨胀的,100度与36度相比,100度时水的密度更接近于冰的密度,因此结冰更快,分子结构重组过程少。
    Reason as follows:The structure of water is different in different temperature.As we all know when water freezen,its volume will inflate.100℃ compared with 36℃,the density of 100℃ water is more close to the density of ice so as to be freezen faster.

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