As someone who has been spending the last week or so at a cushy temp job reading old Straight Dope columns, I feel it is finally my time to speak up.
The myth that hot water freezes faster than cold is actually a misunderstanding, as so many of these things are. While hot water won’t freeze faster than cold, tap water that is boiled first and allowed to cool will freeze faster than a sample of water at the same temperature that wasn’t initally boiled. This is because your run-of-the-mill tap water contains lots of dissolved gas, mainly oxygen, nitrogen, and carbon dioxide (air). Boiling the water removes these gases, thus creating purer water. As any good student of chemical thermodynamics will tell you, impurities tend to hinder crystal formation. Topics like this tend to take entire thesis to fully explain, but essentially for a crystal of ice to form, the molecules have to arrange themselves in a lattice. When impurities are present, they can block positions in the lattice, and the freezing molecules have to wait for them to get out of the way.
There’s also the added complication of impurities lowering the freezing point of any given liquid.
Not the most exciting of debuts to this message board, but you’ve got to go with ya got.
Yes, I am aware of the column. However, my point was that the myth of hot water freezing faster than cold water was in fact just a misunderstanding of what is in fact true.
[[Yes, I am aware of the column. However, my point was that the myth of hot water freezing faster than cold water was in fact just a misunderstanding of what is in fact true.]]
We know you’re aware of the column, but it’s good to link to it, so others can read what you’re responding to.
After reading these messages about how hot water does not freeze before cold and Cecil’s piece on really hot water vs hot water, I need to set the record as straight as possible.
Hot water has been proven through many scientific experiments to freeze before cold water. This is called the Mpemba Effect. This effect has been observed since Aristotle’s time. Although scientists agree whith this effect, they can not agree on one reason why it happens. The issue about evaporation brought up in Cecil’s response is not entirely accurate. A covered beaker will still show the Mpemba Effect, and the original experiment by Mpemba and Osborne (the creators of this effect) calculated the mass of evaporated water to be not enough to drastically change the outcome of the experiment. Although evaporation most likely has to do with it, it is not everything. This is the key mistake everyone makes when it some to this issue. THERE IS NO ONE CAUSE. So there you have it. Although this is not widespread knowledge, it is a fact. Check out these sites for more information and I more indepth analysis. This is a great source
And here is Cecil’s original response. I hope he reviews this issue to help set the record straight. Cecil’s original response
The fridge we had when I was a child had metal ice cube trays sitting on a shelf which had circulating coolant tubes welded to their underside. I think this was a common configuration then. If you put trays full of hot water in them the tray and shelf would weld themselves solidly together. This would greatly facilitate heat transfer. I suspect the “myth” was once true, but is no longer.