Know why hot water freezes faster than cool water?

[fisharmor]

A simple explanation to this;

More energy is transferred during the same time interval when the difference in temperature is bigger.
So when the surrounding temperature is far below freezing, boiling or hot water will lose energy much more rapidly.
In some cases, where there is enough temperature difference, this will make hot water pass freezing temperatures faster, as cooler water.

If the heat conductivity is known, the mass and temperature of the water are known, and the surrounding temperature. One can calculate and draw a curve for the temperature of each vessel of water filled with different temperature water. When calculating which of these two vessels and their intersection with freezing point, it is known which will freeze first.

Did they really give away a 1000$ ? They made me do calculations like this in high school.

This is where my mind was going, only slightly differently.
I'm wondering if anyone has taken specific measurements of the temperature of the ice when it phase transitions.
My hypothesis would be that the hot water freezes at a higher temperature than does the cold water.

6:37 PM

Both are frozen but not solid. The cold water seems to be frozen harder than the hot water because I was able to poke my finger through the hot water cube but I was not able to poke my finger through the cold water cube. My experiment is not necessarily scientific, but my report is honest.
My findings: Hot Water freezes exactly as fast as cold water.

I think in order to test this you'd have to do it two separate times. Having the water in the same ice tray introduces the possibility that the hot water is affecting the whole environment.

 

[roho76]

Is it pure DI water or straight tapwater?

Bingo.

 

[FindLiberty]

Fun in very COLD outdoor temperatures: (this works at -10 degrees F., but I'm not sure of the exact temperature range.)

When the outdoor temp is way below zero, fill a cup with water while indoors. The water can be at room temp, cold, or even chilled down to a temp that's just above freezing. Step outside and toss the water up into the air. The water splashes out and falls to the ground where it soon freezes into a nice little ice patch. (Do this experiment away from any walkways!)

Next, try the same thing again using boiling hot water in the cup. When you toss out the HOT water... POOF, instant snow and maybe a few small ice crystals appear! The snow slowly floats downward away from a cloud of visible water vapor. There does not appear to be very much snow relative to the amount of water used and it makes an interesting sound as this happens!

 

[liberdom]

it says "start to freeze" , does it mean it freezes completely first too?

the only explanation I can think of (and it's probably wrong) is that hot water has greater molecule mobility, so the hot water molecules are circulating and cooling down faster than the cool cup's molecules.

If your goal wasn't freezing, and simply cooling down, to say, 20C. You may expect that the 100C water to drop down to 20C at a rate faster than the 35C water, but not necessarily achieve 20C faster.