Why does hot water freeze quicker than cold water under certain circumstances?

Question

You would think that cold water would freeze quicker because it is closer to freezing point than the hot water.

This has puzzled me for a number of years.

Answer 1

http://www.apnoia.org/ivantic/fizika/faq...

Answer 2

In a tightly controlled setting, i.e. two sealed containers, the cold water would freeze first because it has less heat to lose.  However, many real-life situations could cause the reverse to work.  The two main ways I'm familiar with for steaming hot water to freeze faster than just warm water are: 1) the steaming hot water will lose some of its volume to evaporation, which means the remaining water will have to lose less heat to freeze, or 2) putting hot water into the freezer will usually cause the freezer to kick on.  A running freezer will blow about the frigid air, causing things to freeze much faster than when it's simply sitting still.  Hope this helps solve your mystery.  :-)

Answer 3

It has puzzled alot of people.  The problem is connected to how this is done; the usual comparison is between two trays of water in a freezer.  The cold water freezes more slowly because there is a layer of frost on the freezer surface that slows the heat transfer from the water to the freezer (heat is transferred, not cold).  The hot water could freeze faster because the frost insulation layer is melted, and heat transfer occurs at a faster rate.

Answer 4

google it



or just think of the molecules in each of the waters which would = common sense

Answer 5

Here I am just giving the approach on how you can look at this matter in a different way. It's gets a bit technical so you might want to go to wikipedia a couple of times.

Usually the rate of any process is determined by the rate constant (say k). (NOTE: it is only constant with respect to concentration of reactants and products)

usually k is a function of the change in "Gibbs free energy". In any process Gibbs free energy tends to go to minimum possible value.

so k = f(G)

also dG = dH - TdS, where G is Gibbs free energy, H is enthalpy, T is temperature and S is entropy (refer to wikipedia)

Now the point which was made by the asker that cold water is closer to freezing point than hot water. By that you simply mean that change in H is larger for hot water freezing as compared to cold water freezing. (note: my statements are not foolproof, but there are cases when we can make these assumptions under suitable approximations)

so in fact the rate is affected by H, T, S and other system parameters. Its true that based on H only cold water should freeze quickly, but it "maybe" possible to create conditions of T and S such that and other parameters such that the overall effect is that hot water freezes quicker.

There is still advanced research going on in thermodynamics, so you can dig into this matter as much as you want if you follow these basic laws (equations) that I just mentioned above.

I know this is a lot different than the kind of approach the others and yourself have taken. You went for the more analytical aspect of it and I went into the mathematical aspect. But note that usually analytical reasoning comes from mathematical results and not in the opposite way.

So the analytical part I leave to you, just make sure your math is right.

Hope this didn't make things worse!!