Which type of water freezes faster?

It may sound surprising, but under certain conditions, hot water freezes faster than cold water. This phenomenon is known as the Mpemba effect, named after Erasto Mpemba, a Tanzanian student who observed it in 1963 during an ice cream-making experiment. Although it seems to go against common sense, the effect has been confirmed by many scientific studies.

The Mpemba effect does not always occur, but when it does, several physical factors help explain it. First, evaporation plays an important role. Hot water evaporates more quickly than cold water, which reduces its total mass. With less water left, freezing happens faster.

Another reason is convection currents inside the water. Hot water develops stronger circulation within the container, which allows it to cool more evenly compared to cold water, where temperature differences can slow down the freezing process.

Additionally, dissolved gases in water may influence the freezing point. Hot water releases gases such as oxygen and carbon dioxide during heating. When these gases are reduced, the freezing behavior changes, sometimes allowing hot water to freeze faster than cold water.

It is also linked to supercooling, a state where water cools below its normal freezing point without turning into ice. Cold water is more likely to supercool before forming ice crystals, while hot water tends to freeze more directly once it reaches freezing temperatures.

It is important to note that hot water does not always freeze faster than cold water, but under specific conditions, the Mpemba effect can be observed. This makes it an interesting and sometimes puzzling concept in physics, especially in the study of thermodynamics, heat transfer, and molecular behavior of water.

Thus, the correct answer is Hot water, because of the Mpemba effect and the scientific principles that influence the freezing process.