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Does Hot Water Freeze Faster Than Cold Water?
4th Grade

This experiment was writen by my daughter for a 4th grade science fair project. The purpose of this experiment was to find out if hot water freezes faster than cold water and if people can save time by using hot water to freeze ice cubes.

The hypothesis for this experiment was "I think that cold water will freeze faster then hot water because it is already cold and will take less time to get to the freezing temperature of 32 F."

Materials:

2 plastic ice cube trays labeled "Hot" and "Cold" with 14 individual cubes.
A freezer (the type found in the average home) with an inner temperature of 19 F
Water from the average home faucet
A Digital Food Thermometer
Analog Clock

At 1:30 p.m I ran the faucet until the water was cold and I filled the ice cube tray labeled "Cold." Then I turned the cold water off and the hot water on. I ran the faucet until the water turned hot and filled the ice cube tray labeled "Hot." I placed the thermometer into the cold water in the cold ice cube tray. When the dial stopped moving I recorded the temperature; it measured at 60 F. I repeated this procedure for the hot water; it measured at 103 F.

Every 30 minutes I measured the temperature of the cold-water tray and the hot-water tray. When the temperature of both trays reached 33 F and ice crystals started to form I knew that I could not measure water temperature anymore since any lower and the water is no longer water but has become ice. The water temperature won't reach below 33 F. I then started checking the trays every 60 minutes for solidity. For the first 4 hours the ice cubes were forming ice crystals only and it was difficult to determine which tray was freezing faster. I continued to check every 60 minutes to determine how many cubes were achieving solidity. The remainder of the time spent on this project was simply to see which tray solidified completely first. The experiment ended at 10:45 p.m.

At the beginning of this experiment I determined that cold water would freeze faster then hot water simply because it would take more time for the hot water to reach the level of freezing. But, as the data shows, the hot water temperature dropped rapidly and within 1 hour of the start time the hot water and cold water had reached the same temperature of 40 F. Both hot and cold maintained the same temperature for the next hour.

From that point on, the hot water appeared to have ice crystals forming faster and when the cubes started to achieve a level of solidity, the hot water did have more cubes freeze then the cold water. By the end of the experiment the hot water had all of its cubes frozen first. However, hot won the "freezing-race" by only 15 minutes. If a person wanted to freeze ice cubes quickly in time for a party or just to have a cold drink, using hot water is not going to be a quick shortcut. It still takes approximately 9 hours to freeze ice cubes regardless of whether hot or cold water is used.

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