Why hot water freezes faster than cold water: The Mpemba Effect

Ever wondered why hot water freezes faster than cold water?

You’re not alone!

For centuries, this question has boggled the minds of brilliant scientists all across the world. This phenomenon, known as the Mpemba Effect, was named after Tanzanian student Erasto Mpemba, who stumbled upon this fascinating discovery in 1963.

However, many believed that the effect was in fact first observed way back in history - during 4th century BC by the famous philosopher, Aristotle.

Counterintuitive yet absolutely intriguing, let’s dive in for a closer look at this mysterious paradox, shall we?

How it all began

It all started as an innocent attempt to nab the last available ice tray during Science class. Eager to secure a spot for his ice cream mix in the small students’ refrigerator, Erasto opted to skip the long wait.

Instead of watching his milk-and-sugar concoction cool to room temperature like the rest of the class, he stuck his hot mixture right into the fridge.

To his pleasant surprise, his mixture froze into ice cream after an hour and a half, whereas those of his more patient classmates remained a thick liquid.

In no time, this accidental discovery drew the eyes of the scientific community and sparked a series of experiments that sought to provide an explanation for this strange phenomenon.

The science behind it

It all boils down to heat energy.

When you put a pot of cold water on the stove, energy from the flame is transferred to the molecules in the water. This extra energy makes them move faster, so they take up more space and become less dense than cold molecules.

When you put both pots of hot and cold water in the freezer, the hot molecules start off with more energy than their colder counterparts. This means they need to lose less energy before they reach their freezing point — making them freeze quicker! 

Another factor is evaporation. Colder liquid has a higher surface tension (the force of molecules sticking together) than hotter liquid does — meaning that warm liquid evaporates faster than cold liquid does. When evaporation occurs during freezing, some of the heat escapes as well — which means even more cooling for your warm liquid! 

Lastly, hot water may have different concentrations of dissolved solids compared to cold water, which could impact the rate of cooling and freezing.

Real-world uses

Beyond delicious ice cream, the Mpemba Effect has practical applications in many different fields. For example, engineers and scientists who work in the refrigeration and cooling industry can use the Mpemba Effect to develop more efficient cooling systems.

By understanding the science behind the Mpemba Effect, they can design systems that freeze water faster, reducing the time and energy required to cool food and other products.

Conclusion

So there you have it - now you know why hot water freezes faster than cold water! Thanks to Erasto’s observations, next time you’re making ice cream for a party and your friends arrived earlier than expected, just remember the power of the Mpemba Effect!