Why does hot water freeze in a shorter amount of time than cold water when in the same environment?

Answer 1

I think it is still an unsolved problem as someone here suggested. I think if you try this experiment yourself you will find varying results, you won't always see the warmer water freeze first. It is called the Mpemba effect http://www.weburbia.com/physics/hot_water.html
Some of it can be explained by the fact that when you put hot water into your freezer, the freezer heats up and so it switches on to cool down again. So the freezer gets colder quicker than if you just put some cold tap water in to freeze and the temperature sensor doesn't start the freezing cycle. You have to be careful about what variables are changing when you perform this experiment. Try it.

Answer 2

Doesn't the hot water--at some point in the process--arrive at the same temperature that the cold water had from the beginning? And wouldn't the two amounts of water then need the same additional time to freeze?

Answer 3

I read about this one time because I found that to be rather interesting and it has something to do with the hot water having molecules that move faster, therefore the cold will move faster through the whole amount of water. Therefore the core will freeze faster.

When the water is cold, the outside will freeze, but the inside cools slower. therefore the core freezes slower.

Still not sure if I understand it, but I do not have enough physics background to dispute it.

Answer 4

Bruce is right. Hot water has to be colled down to the cold water and freezes. Therefore hot water can not freeze fsater than the cold water under same conditions.

Answer 5

Hot water freezes faster than cold water because the air has been removed in the heating process. The air in cold water acts as a thermal buffer.

Answer 6

Common myth spurred by a discovery. The discovery is refrigeration.

First, you are ABSOLUTELY WRONG!

Next, there is only one documented case where you could be correct. In a freezer, there are thermal sensors that detect when to turn on the system. If boiling water is placed into the freezer, these sensors trip and turn on the freezer nearly immediately. Therefore, the freezer cools off the water faster. If cool water is placed into the freezer, it takes a MUCH longer time to trip the same sensors and thereby the water freezes slower.

Answer 7

If hot water is water with a temperature greater than 20 degrees Celsius, I would think it would be hard for it to freeze at all. It is my understanding that hot water does not freeze.

Answer 8

From what I understand, scientist don' really know EXACTLY why.

And it doesn't allways happen. The container, starting temperaure, and temperature of environment affect this.

My guess is the hot watter has a head start. Since the temperatures are exremes it cools much faster and just keeps cooling, while the cool waer changes slower.