Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne rates of freezing
Name: N/A
Status: N/A
Age: N/A
Location: N/A
Country: N/A
Date: N/A

I should know the answer to this question. So should the physics and chemistry teachers at our school, but they disagree. I have heard two, perfectly good explanations with different "facts". Here goes..... DOES hot water freeze faster than cold water? (You were expecting something really good were not you?) If so, why? If not, why? Somebody's gonna have to eat crow. (I am glad that I did not express my opinion - but I will bet I am right!)

First, I think scientifically you should qualify your 'hot' or 'cold' description by temperature, in any scale of your choice (i.e. Fahrenheit, Celsius, or Kelvin). Given that, however, I will assume that your 'hot' water is higher in temperature than your 'cold' water. Assuming no dissolved impurities which might other- wise affecting the freezing (melting) point of said water, I will place my bet and say that since the 'hot' water, by definition contains more energy and therefore more molecular motion, it would freeze more slowly (i.e. would require more cooling to get down to the freezing point) than the water you describe as 'cold'. The 'cold' water , containing less energy (by definition) and therefore less molecular motion should require less cooling to get to the freezing point. I would like to hear both sides of the opinions of your faculty.


Yes, hot water in a freezer freezes fast than cold water, as every competent houseperson (formerly,"housewife") knows. The reason is that the surface of the freezer usually has a layer of ice on it. Ice is an excellent insulator, and therefore limits the heat transfer to the freezing surface. Putting hot water in your pan (or ice-cube tray) has the effect of melting the ice-layer on the surface, providing for better heat transfer to the surface. There is also the fact that there is increased evaporation from the warm water, which reduces the mass of water that must be cooled, as noted in item 3.40 of Jearl Walker's book "The Flying Circus of Physics." That book is the first place to look for answers to questions of the type that you posed.

Jack L. Uretsky

Jack L. Uretsky, You will recall that the question was does hot water freeze faster than cold water. I don't recall it mentioning a freezer, nor a coating of ice, nor allowing for escape of some of the targeted hot water to freeze. I maintain my answer as correct, given the question that was asked. Naturally if heat is allowed to escape from the system, either thru melting of a supposed coating of ice or warming of some freezer space, than your assertion might change the scenario. In a laboratory with a controlled experiment where all the heat is accounted for, I believe you will find my answer to be the correct one , i.e. cold water will freeze faster than an equivalent quantity of hot water.


Click here to return to the Physics Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (, or at Argonne's Educational Programs

Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory