Mpemba effect

Source-This post is based on the article “Mpemba effect: Heat up to cool down” published in “The Hindu” on 22nd January 2024.

Why in the News?

The Mpemba effect has recently captured the attention of scientists. After many experiments, we still don’t have a clear agreement, on what causes this puzzling phenomenon.

What is Mpemba effect?

1) It is a phenomenon in which hot water freezes faster than cold water under certain conditions.

2) It is named after Tanzanian student Erasto Mpemba, who observed it in the 1960s.

What are the recently proposed causes for this phenomenon by scientists?

1) Presence of Microbubbles- One of the proposed causes is the presence of microbubbles that remain suspended in water after boiling. These microbubbles promote convection and facilitate faster heat transfer. Hence, the warm water cools down more quickly.

2) Evaporation- Another cause is attributed to evaporation. As warmer water evaporates more, it takes away the heat more quickly. Thus, warm water cools down more quickly as compared to cold water.

3) Presence of Frost in Cold Water- The presence of frost in cold water acts as an insulator which impedes/slows down the process of heat loss. This raises the freezing point of cold water.

4) Presence of Calcium carbonate and other impurities- Compounds like calcium carbonate precipitate in warm/hot water, and it lowers down the freezing point of warm water. On the other hand, in cold water, calcium carbonate and other impurities remain dissolved in the cold water, which increases the freezing point of cold water.

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