Hot Water Freezes Faster Sometimes

It seems to defy common sense, but a container of warm water can, in some cases, turn to ice before an identical container of cool water. This puzzling phenomenon gained modern recognition through the curiosity of a Tanzanian schoolboy. In 1963, while making ice cream for a class project, Erasto Mpemba noticed his hot mixture froze solid in the freezer before the cooler batches prepared by his classmates. Initially dismissed by his teacher, his persistent observation was later confirmed by a university physicist, lending his name to the "Mpemba effect."

While Mpemba brought the effect to the attention of modern science, observations of it date back centuries to thinkers like Aristotle and René Descartes. The exact reason it occurs is still a subject of scientific debate, as it doesn't happen in every single trial. Scientists believe it's not one single cause, but a complex interplay of factors. Leading theories suggest that the warmer water evaporates more quickly, reducing the total mass that needs to freeze. Other explanations point to the role of dissolved gases, which are expelled from hot water, or to differences in how convection currents transfer heat. The hotter water might also avoid "supercooling" (dropping below 0°C without solidifying), allowing it to freeze at a higher temperature than its colder counterpart.