Cold Water or Warm Water - Which Freezes Faster

[deleted-36419]

Hello I have completed my science project on which freezes faster, cold water or warm water. Part of my project requires me to get the opion of a professional. Can you tell me your opinion as well as your conyact information so I can complete my project.

Thank You,
Brookelynn

[MelissaB]

Hi,

Science Buddies prohibits posting of contact information. See here: https://www.sciencebuddies.org/mentorin ... =25&t=4489 for information regarding interviews and Science Buddies. I suggest you contact a professional in your hometown for help.

[deleted-71588]

If you have the same amount of truely identical water in truely identical containers and the only difference is one container and contents is hotter than the other, it will take more time to freeze than the cooler container and contents.

If there are any differences in the containers or the water, then I have no opinion. Note: Hot and cold tap water may not be identical. The typical hot water heater is a big tank that collects preciptates in the bottom and may undergo some electrolysis if there is an electric heating element in the tank and a manganese sacrificial annode.

Note: Cooks typically add salt to water to depress the boiling point so that it takes less heat/time to get to the boiling point. Salts typically will also depress the freezing point. If the hot tap water came through a water softner with a salt regeneration resin filter bed, and the cold water didn't, then there will be a chemical difference in the water sources.

[deleted-71487]

It's a counter-intuitive result, but many examples have been shown of cases where, in certain conditions, warmer water can freeze faster than cooler water. It's usually referred to in modern times as the Mpemba effect, though apparently Aristotle noticed it, too.

Here are a few examples of discussions of this effect, with some references (note: the web is a good place to *start* research, but you should rely on what anyone says without checking references):

http://math.ucr.edu/home/baez/physics/G ... water.html
http://www.gi.alaska.edu/ScienceForum/ASF6/650.html
http://www.school-for-champions.com/science/mpemba.htm

It doesn't appear that anyone really knows what, exactly, causes this effect (which makes it a really good experiment... if you isolated the cause that'd be very cool). There are many theories, but it's a subtle effect and water freezing is subject to a large number of variables, including gas content of the water (which is driven down by heating), conduction with the metal shelf of the freezer (which might be better if any ice on it is melted by hotter water and allowed to drip away), increased evaporation of the warmer water (possibly reducing its mass), etc., etc.