This question continues to generate considerable controversy. Takamasa Takahashi, a physicist at St. Norbert College in De Pere, Wis., tries a definitive answer:
“Cold water does not boil faster than hot water. The rate of heating of a liquid depends on the size of the temperature difference between the liquid and its surroundings (the fire on the stove, for instance). As a result, cold water will be absorbing heat quicker while it is still chilly; once it becomes up to the temperature of hot water, the heating rate slows down and from that point it takes just as long to deliver it to a boil since the water that was warm to start with. Because it requires cold water some time to make it to the temperature of warm water, cold water clearly takes longer to boil than warm water does. There can be some psychological impact at play; cold water begins boiling sooner than you might expect due to the aforementioned greater 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 generally, but possibly under specific conditions.’ It takes 540 calories to vaporize one gram of water, whereas it requires 100 calories to bring one gram of liquid water from 0 degrees Celsius to 100 degrees C. When water is hotter than 80 degrees C, the rate of cooling with rapid vaporization is very high because each evaporating g attracts at least 540 calories in the water left behind. This is a very large quantity of heat as well as the one calorie per Celsius degree that is drawn from every gram of water which cools by routine thermal conduction.
“It all depends on how quickly the cooling happens, and it ends up that hot water won’t freeze until chilly water but will freeze before lukewarm water. Water at 100 degrees C, for instance, will freeze before water warmer than 60 degrees C but not until water cooler than 60 degrees C. This phenomenon is particularly evident when the surface area that cools by rapid evaporation is substantial compared with the amount of water involved, like if you wash a car with warm water on a cold winter day. [For reference, consider Conceptual Physics, by Paul G. Hewitt (HarperCollins, 1993).]
“Another situation in which warm water may freeze faster is when a bowl of cold water along with a pan of warm water of equivalent mass are placed in a freezer compartment. There’s the effect of evaporation mentioned above, as well as 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), subsequently near-freezing water in the base increases to the surface. Convection currents will last until the entire body of water is 0 degrees C, at which time all the water eventually freezes. If the water is initially hot, cooled water in the base is denser than the hot water at the top, so no convection will occur and the base part begins freezing while the surface is still warm. This effect, combined with the evaporation impact, can make hot water freeze faster than cold water sometimes. In cases like this, naturally, the freezer will probably have worked harder during the specified time period, extracting more heat from warm water.”
Robert Ehrlich of George Mason University, in Fairfax, Va., adds to some of the points created by Takahashi:
“There are just two methods by which warm water could freeze faster than cold water. 1 way [described in Jearl Walker’s book The Flying Circus of Physics (Wiley, 1975)] depends on the fact that warm water evaporates faster, so if you began with equivalent masses of hot and cold water, there would soon be less of the hot water to freeze, and therefore it might overtake the chilly water and freeze first, since the lesser the mass, the shorter the freezing time. Another way it could occur (in the case 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, resulting in a better thermal contact when it refreezes.”
Read more here: http://www.nemetvolgyiantikvarium.hu/2019/10/15/cobb-packers-an-ex-girlfriend-that-broke-up-with-you/