reason why hot water freezes faster

Cecil's Columns/Staff Reports
1

I’ve always been told that there is always a small truth in every old wives tale…
Here is where this hot water boils faster…

In the old days of having freezers WITHOUT automatic defrost cycles, there would be a coating of ice crystals on all inside racks, wire freezer coils, etc. So much ice was formed that you would have to DEFROST the inside every so often. (remember this you older baby boomers?) AND before the advent of PLASTIC ice cube trays, there were METAL trays with a complicated metal lever that would break and eject the trays. So, where is all this going?

If you fill a METAL ice cube tray with hot water and place it on a ice covered wire freezer coils , the heat would melt the frost allowing the metal ice cube tray to come in better physical contact with the freezer coil allowing the water to freeze faster. (Cold water ice cube trays would rest on top of the frost covered freezer coils and not have the better contact with the freezer coils. )

So, if you filled one metal tray with hot water and one metal tray with cold water, and put them both on top of frost covered freezer coil, the hot water one WOULD freeze faster.

So, in these old days, we would be told "Of course, hot water freezes faster than cold. " and the story continued to be handed down.

PHYSICS!

2

Welcome to the Straight Dope Message Boards, dal9000, we’re glad to have you with us.

When you start a thread, it’s helpful to other readers if you provide a link to the column you’re discussing. Saves search time and helps keep us all on the same page. In this case, I assume, it’s: Which freezes faster, hot water or cold water? - The Straight Dope

Also of tangential interest: Which boils faster, hot water or cold water? - The Straight Dope

Anyhow, no big deal, you’ll know for next time. And, as I say, welcome!

3

I’m a little skeptical of this bit. Cold tap water is still well above freezing. The cold water could also be warm enough to melt through frost.

Does anyone know of any testing of whether this explanation actually has any validity?

4

It sure does. I used to put metal baking pans of hot water on my frost-filled refrigerator freezer to melt the frost away. It was easier to melt away some of the ice and frost first rather than chipping away at it or unplugging it for a few more hours. It never got rid of ALL of it, but it would melt down to the coils most of the time. I remember reading about the Mpemba effect and trying it out. Well the hot pan was frozen solid and stuck to the coils, and the cold one sat on top of the frost and was partially frozen. There was about an inch of frost on the coils to start.

5

Interesting sidebar…my ‘findings’ over the warm-water-hot-water-cold-water-ice-cube-freezing-rate-debate:

–whether or not you think warm to hot water freezes faster is irrelevent if you like your ice-cubes whole–here’s why–

I had a friend(she was around 65y/o and filled with old wives tales!) and she swore by her warm-water-freezes-ice-cubes-faster theory. But I noticed one thing about her ice…IT ALWAYS FELL APART IN MY GLASS!

I hate taking sips off a soda and advertantly choking on a sliver of ice. :smack: So I rarely used her ice. I decided to do my own testing. And every time I used warm water for my ice, the cubes would crack into slivers.

I lived in Framingham MA at the time, and it may have had something to do with whatever the town treated the public drinking water with. But for me, there’s no substitute for using cold spring water from the fridge to make ice cubes!