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

This simple question continues to generate controversy. Takamasa Takahashi, a physicist at St. Norbert College in De Pere, Wis., tries a definitive answer:
“Cold water doesn’t boil quicker than hot water. The rate of heating of a liquid is dependent upon the magnitude of the temperature difference between the liquid and its environment (the flame on the stove, for example ). As a result, cold water will soon be consuming heat quicker while it’s still chilly; after it becomes up to the warmth of warm water, then the heating rate slows down and from that point it takes as long to bring it to a boil since the water that was hot to begin with. Because it takes cold water some time to reach the temperature of warm water, cold water clearly takes longer to boil than warm water does. There may be some psychological effect at play; cold water starts boiling sooner than you might expect because of the aforementioned higher heat absorption rate when water is colder.
“To the first part of the question–‘Does hot water freeze faster than cold water?’ –the answer is’Not generally, but maybe under specific conditions.’ It takes 540 calories to vaporize 1 g of water, whereas it takes 100 calories to bring 1 gram of liquid water from 0 degrees Celsius to 100 degrees C. When water is warmer than 80 degrees C, the rate of cooling by rapid vaporization is quite high because every evaporating gram draws at least 540 calories from the water left behind. This is a very large amount of heat as well as the 1 calorie per Celsius degree that is drawn from each gram of water which cools by regular thermal conduction.
“It all is dependent upon how fast the cooling happens, and it turns out that hot water won’t freeze until chilly water but will freeze until lukewarm water. Water at 100 degrees C, by way of example, will freeze until water warmer than 60 degrees C but not before water cooler than 60 degrees C. This phenomenon is particularly evident when the surface area that cools by accelerated evaporation is substantial compared with the amount of water involved, such as if you wash a vehicle with hot water on a chilly winter day. [For reference, consider Conceptual Physics, by Paul G. Hewitt (HarperCollins, 1993).]
“Another situation where hot water may freeze faster is when a pan of cold water and a pan of hot water of equivalent mass are set in a freezer . There is the effect of evaporation mentioned above, and also the thermal contact with the freezer will cool the bottom region of the body of water. If water is cold enough, close to four degrees C (the temperature at which water is densest), then near-freezing water in the base will rise into the top. Convection currents will continue until the whole body of water is 0 degrees C, at which point all the water finally freezes. If the water is hot, cooled water in the base is thicker than the warm water on top, so no convection will happen and the base part will start freezing while the top remains warm. This effect, together with the evaporation impact, can create hot water freeze faster than cold water in some cases. In cases like this, of course, the freezer will have worked harder throughout the given amount of time, extracting more heat from hot water.”
Robert Ehrlich of George Mason University, in Fairfax, Va., adds to some of the things made by Takahashi:
“There are two methods by which hot water can freeze faster than cold water. One way [described in Jearl Walker’s book The Flying Circus of Physics (Wiley, 1975)] is determined by the fact that hot water disappears faster, so if you started with equivalent masses of warm and cold water, there would soon be less of the hot water to freeze, and hence it might hamper the cold water and freeze first, because the lesser the mass, the shorter the freezing time. The other way it may occur (in the case of a flat-bottomed dish of water set in a freezer) is when the warm water melts the ice under the bottom of the dish, then leading to a superior thermal contact when it refreezes.”

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