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

This question continues to generate considerable controversy. Takamasa Takahashi, a physicist at St. Norbert College in De Pere, Wis., tries a definitive response:
“Cold water does not boil quicker than hot water. The rate of heating of a liquid depends on the size of the temperature difference between the liquid and its environment (the flame on the stove, for instance). As a result, cold water will soon be absorbing heat faster while it’s still cold; once it becomes up to the warmth of warm water, then the heating rate slows down and from there it takes as long to deliver it to a boil since the water that was hot to start with. Because it takes cold water some time to make it to the temperature of hot water, cold water obviously takes longer to boil than hot water does. There may be some psychological impact at play; chilly water begins boiling sooner than you might expect due to the aforementioned greater heat absorption rate 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 maybe under specific conditions.’ It takes 540 calories to vaporize one g of water, whereas it requires 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 each evaporating gram attracts at least 540 calories in the water left behind. This is a really large amount of heat compared with the one calorie per Celsius degree that is drawn from each gram of water which cools by routine thermal conduction.
“It all is dependent upon how fast the cooling occurs, and it ends up that hot water won’t freeze until chilly water but will freeze before lukewarm water. Water at 100 degrees C, by way of example, will freeze before water warmer than 60 degrees C but not until water cooler than 60 degrees C. This phenomenon is especially evident when the surface region that cools by accelerated evaporation is large compared with the amount of water required, 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 in which hot water can freeze faster is when a bowl of cold water along with a pan of warm water of equal mass are placed in a freezer compartment. There’s the impact of evaporation mentioned above, and also the thermal contact with the freezer will cool the base 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 at the bottom will rise to the surface. Convection currents will last until the whole body of water is 0 degrees C, at which time all the water eventually freezes. If the water is hot, cooled water in the bottom is thicker than the hot water at the very top, so no convection will happen and the bottom part begins freezing while the surface is still warm. This effect, together with the evaporation effect, may create hot water freeze faster than cold water in some cases. In this case, naturally, the freezer will probably have worked harder during 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 created by Takahashi:
“There are just two ways in which hot water could freeze faster than cold water. One way [described in Jearl Walker’s novel The Flying Circus of Physics (Wiley, 1975)] is determined by the fact that warm water evaporates faster, so that if you began with equal masses of warm and cold water, there will soon be less of the hot water to freeze, and therefore it might hamper the chilly water and freeze , since the lesser the bulk, the shorter the freezing time. The other way it may happen (in the case of a flat-bottomed dish of water placed in a freezer) is when the hot water melts the ice below the base of the dish, resulting in a superior thermal contact when it refreezes.”

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