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Why does hot water freeze quicker than cold water? Answered



It doesn't.

It is a myth.


9 years ago

because when you put something cold in a hot environment it causes condensation or vise versa, a hot ice tray in a feezer for example is going to build up condensation, on the outside of the tray which will then evaperate speeding up the cooling process. I used to work as a plumber, hot water pipes will freeze faster then cold water pipes in the winter for the same reason. When it is really cold you will notice water condinsation on the out side of your hot water pipe but not on the cold water pipe, that then starts the pipe freesing faster do to evaporation, like if you your finger and then blow on it you finger gets cool because as the water evaporates it takes heat with it. I good way to demontrate this is to get two glasses fill both with water of the same temperature then rap a wet papertowel around one of the glasses then put both glasses in the freezer, the glass rapped in the wet paper towel should freeze faster because as the water evaporates from the wet paper towel it will take heat from the glass with it starting the ice crystals to form faster.

*like if you lick your finger and blow on it

we talked about this in physics, its one of newtons laws that the greater the temp. diff. the faster it will cool down or heat up. hope that helped

As CameronSS says, the physical basis for the Mpemba effect is a matter of much speculation and hypotheses.

The temperature difference can't be too large (or the obvious argument about time-to-cool is correct), and the water conditions have to be carefully controlled. If you set up your experiment carefully to meet those conditions, then the Mpemba effect is measurable and reproducible.

In most instances, it doesn't. However, it can. The answers given below have been shamelessly stolen from Monwhea Jeng at the University of California:

  • Hot water will lose mass to evaporation while it is being cooled, and therefore effectively has less mass to cool. Also, the evaporation process is endothermic, i.e., it requires heat energy, which further cools the water.
  • One possible, but not proven, reason is that hot water holds less dissolved gas than cold water. No one seems to have ever given any reasoning for this, though.
  • The hot water will tend to set up a faster convection system than the cold water, due to the loss of heat at the surface of the container. The faster convection can cause it to cool faster.
  • In some circumstances, the hot water may affect the surrounding environment in ways that cause it to absorb heat, such as if the containers are sitting on frost that might be melted by the hot water.

In other words, no one really knows for sure.