Since boiling water freezes faster than cold water, does it stand to reason that any hot water will freeze faster than water colder than it?
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Answer:
What you're referring to is the "Mpemba Effect." In 1963, Erasto Mpemba, a Tanzanian (then Tanganyikan) high school student noticed that when he attempted to freeze ice cream mix in cooking class, it worked faster if he started with hot mix than with cold mix. He asked a university professor why this happened and was roundly mocked - only to have his observation confirmed by the university professor. Six years later, they published on it. We know very little about the Mpemba Effect. We know that under certain circumstances, hot water freezes (or reaches 0 degrees Celsius, the two are not the same, but documentation of the effect has referred to both) first, but we have virtually no idea as to what conditions must exist for it to take place. For example, it appears with tap water, you're better off starting with 35 degrees Celsius for the hot water and 5 degrees Celsius for the cold water, but whether solute concentration, container shape, gas concentration, freezer temperature, etc. changes things is, as yet, unknown. However, we do know that the Mpemba Effect does not always manifest. Hot water does not always freeze first. Because of this and because we do not know the mechanism by which the Mpemba Effect works in the first place, we can't really make the assumption that "hotter water always freezes before colder water."
Harold Kingsberg at Quora Visit the source
Other answers
No. The Mpemba effect is bogus. Hot water contains more kinetic energy than cold water and hence will take longer to freeze on average if the experiment is properly controlled.
Anirudh Joshi
I always thought the idea of hot water freezing is ridiculous. Hot water does not freeze. It must first become cold water before it can freeze. The Mpemba effect is a mystery to this day, but under most circumstances "water that started out hot" will not freeze faster than "water that started out cold." With our experiments, we used four temperatures, cold tap water (~45F), lukewarm water (~70F), hot tap water (~140F) and boiling water (212F), and surprise surprise, they each formed a layer of ice in the order of coldest to hottest. We did not monitor whether the hottest sample completely froze before the coldest sample did - it looked like the cold sample had far more ice. The statement that "Hot water freezes faster than cold" is inaccurate in 95% of the cases, maybe more. Hot water does not freeze. It must first become cold. In order to claim that a hot water sample will freeze faster than a cold water sample, you must first define "hot" and "cold" -abstract terms. Are we talking steam? It's very likely that a container of steam would freeze faster than a cup of cool/lukewarm water. The hot water sample must surpass the temperature of the cold sample. For instance, I could take the claim that "hot water freezes faster than cold water" and say that a cup of ice IS cold water, and your claim is incorrect. Or, I could take a cup of water 32.5F and boiling water and also guarantee that the cold will freeze first. (Look up the examples of pure, supercooled water still in liquid form because the molecules have nothing to bind to, it freezes almost instantly if a condition occurs that allows them to bind, an impact for instance.) Mass is not determined in the claim. (see steam example) Be more specific. Since hot and cold are relative terms, you might say that an ice cube is in fact, hot. At the same time, an ice cube can be said to be cold. In this case, you could be correct and incorrect, depending on your perspective. There's a reason plumbers don't plumb ice machines with the hot water line.
Marty Clevenger
it has happened in number of even controlled experiments but still there is not much explanation for Mpemba Effect. But u cant say that hotter water always freezes before colder water bcoz if suppose cold water is at 2 degree celsius n hot water at 80 degree then obviously cold water will feeeze first
Ayush Tyagi
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