Is It True that Hot Water Freezes Faster than Cold Water or that Cold Water Boils Faster than Hot Water?

This straightforward question continues to generate considerable controversy. Takamasa Takahashi, a physicist at St. Norbert College in De Pere, Wis., tries a definitive answer:
“Cold water doesn’t boil quicker than warm water. The rate of heating of a liquid depends on the magnitude of the temperature difference between the liquid and its environment (the flame on the stove, for instance). As a result, cold water will be consuming heat quicker while it is still chilly; once it gets up to the temperature of hot water, the heating rate slows down and from there it takes as long to deliver it to a boil as the water that was warm to begin with. Because it requires cold water a while to make it to the temperature of hot water, cold water clearly takes longer to boil than hot water does. There can be some psychological effect at play; chilly water starts boiling sooner than one might expect because of the aforementioned higher heat absorption speed when water is colder.
“To the first part of the question–‘Does hot water freeze faster than cold water?’ –the response is’Not usually, but possibly under certain conditions.’ It takes 540 calories to vaporize one g of water, whereas it takes 100 calories to bring one gram of liquid water from 0 degrees Celsius to 100 degrees C. When water is warmer than 80 degrees C, the rate of cooling with rapid vaporization is quite high because each evaporating g attracts at least 540 calories in the water left behind. This is a very large amount of heat compared with the one calorie per Celsius degree that is drawn from each gram of water which cools by regular thermal conduction.
“It all depends on how fast the cooling occurs, and it turns out that hot water won’t freeze before chilly water but will freeze until lukewarm water. Water at 100 degrees C, by way of instance, will freeze before water warmer than 60 degrees C but not before water cooler than 60 degrees C. This phenomenon is particularly evident once the surface area which cools by rapid evaporation is large compared with the total amount of water involved, such as when you wash a vehicle with hot water on a cold winter day. [For reference, consider Conceptual Physics, by Paul G. Hewitt (HarperCollins, 1993).]
“Another situation where warm water may freeze quicker is when a bowl of cold water and a pan of hot water of equivalent mass are placed in a freezer compartment. There is the effect of evaporation mentioned above, as well as the thermal contact with the freezer will cool the base part of the entire body of water. If water is cold enough, near four degrees C (the temperature where water is densest), subsequently near-freezing water in the base increases to the surface. Convection currents will continue until the entire body of water is 0 degrees C, at which point all the water eventually freezes. If the water is hot, cooled water in the base is thicker than the warm water at the top, therefore no convection will happen and the base part begins freezing while the surface is still warm. This effect, together with the evaporation effect, can create hot water freeze faster than cold water in some cases. In this case, of course, the freezer will have worked harder during the given time period, extracting more heat from warm water.”
Robert Ehrlich of George Mason University, in Fairfax, Va., adds to some of the points made by Takahashi:
“There are just two ways in which hot water could freeze faster than cold water. One way [described in Jearl Walker’s book The Flying Circus of Physics (Wiley, 1975)] depends on the fact that hot water evaporates faster, so that if you began with equal masses of warm and cold water, then there would soon be of the hot water to freeze, and hence it would overtake the cold water and freeze first, because the lower the bulk, the shorter the freezing time. The other way it may happen (in the event of a flat-bottomed dish of water placed in a freezer) is if the hot water melts the ice below the bottom of the dish, leading to a superior thermal contact when it refreezes.”

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