KnowHOW team explains: Anomalous it may seem, but it?s true that hot water freezes more quickly than cold water when put in a freezer. Although not acceptable by all scientists, it has been experimentally proved that, in a controlled temperature, hot water solidifies faster than cold water. Tests show that the maximum time taken to solidify in the freezer occurred when its initial temperature was about 5 0C, and the shortest time when it was about 35 0C.

This paradoxical behaviour can be explained by the temperature difference of the water. The rate of heat loss from the upper surface is proportional to the temperature of the rest of the water. If the surface can be kept at a higher temperature than the bulk of the liquid, then that water?s rate of heat loss will be greater than from water with a uniformly distributed average temperature.

The large temperature gap between the hot water and its environs drives a vigorous convective current which continues to pump heat to the surface, speeding up and maintaining the thermal transfer, even after most of the water has been frozen.

The absence of dissolved gases in heated water also contributes to its freezing. Dissolved gases are lost when water is heated. Without these gases, ice crystals can grow faster.

The question was sent by M. Subhash Singh from Imphal