How the Mpemba Effect Works

How the Mpemba Effect Works
One oxygen atom and two hydrogen atoms bond to form a water molecule

Yesterday, I warned of the danger of trying to solve an argument using the scientific method when people want to stick to their preconceived ideas. The argument I referred to was between my family members about whether hot or cold water freezes faster. The truth is that the phenomenon where hot water freezes faster is called the Mpemba effect after an African secondary school student who brought it to the attention of a British physicist. Even though it had been observed since Aristotle’s time, most people didn’t believe it, and nobody seriously attempted to explain how the Mpemba effect works.

Perhaps the reason science ignored the Mpemba effect is because it seems illogical and unreasonable. In 2013, Xi Zhang and colleagues at Nanyang Technical University in Singapore presented a possible solution to how the Mpemba effect works. Water molecules contain one atom of oxygen bonded to two atoms of hydrogen (H2O). The oxygen atom shares an electron with each hydrogen atom in what is known as covalent bonding.

In addition to the covalent bonding within the water molecules, the separate molecules are held together by hydrogen bonds. Water molecules are polarized, and since water is a liquid, the molecules move around. When a hydrogen atom in one molecule is close to the oxygen atom in another molecule, hydrogen bonds loosely hold them together. Hydrogen bonds explain the surface tension of water, its relatively high boiling point, and how the Mpemba effect works.

As water is heated, the molecules move faster, stretching the hydrogen bonds, causing them to store energy, and allowing the covalent bonds to relax and give up some energy. Covalent bonds giving up energy is equivalent to cooling, allowing the heated water to freeze faster. In a 2017 issue of the Journal of Chemical Theory and Computation, Yunwen Tao and co-authors described using vibrational spectroscopy and modeling to show that hydrogen bonds can explain how the Mpemba effect works.

Other factors can be involved in water freezing to counter the Mpemba effect. Dissolved gases or other impurities, convection currents, evaporation, and even the container can influence the time it takes for water to freeze. The relative initial temperatures and consistency of the water samples are also critical factors.

The bottom line is that the design of water is an essential factor that makes life possible. We have said that before: HERE, HERE, HERE, HERE, and HERE. The fact that hot water can freeze faster than cold is hard to believe, but true. Even harder to believe is that the design of water, the universe, our planet, and life could be accidental, but atheists still argue that those designs all happened by chance. I challenge you to carefully consider where you stand on the existence of a creator God.

— Roland Earnst © 2023

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Does Hot or Cold Water Freeze Faster?

Does Hot or Cold Water Freeze Faster?

As a young boy, I learned not to try to solve family arguments between my elders. My father told my aunt (his sister) that he had heard that hot water freezes faster than cold water. She said that could not be true, and that led to a heated argument between them. I thought this was not something worth arguing about, and I suggested that we test the theory by the scientific method. Does hot or cold water freeze faster?

Thinking I could settle the argument, I suggested we fill one ice-cube tray with hot water and one with cold water, put them both in the freezer and see what happens. This suggestion from a young “whippersnapper” brought down the wrath of both sides. I realized that they didn’t want to know the truth. They just wanted to argue. Perhaps they were both afraid they might be proven wrong. I have since learned that believers and skeptics often fear looking at evidence for that very reason.

So, does hot or cold water freeze faster? The short answer is that it depends. Some famous thinkers, including Aristotle, Francis Bacon, and Rene Descartes, noticed that hot water sometimes froze faster than cold water. But it took a Tanzanian secondary student making ice cream in 1963 to finally bring this question into scientific focus.

Young Eraso Mpemba, along with fellow students at Magamba Secondary School, was making ice cream to earn some money. He was in a hurry, so rather than letting it cool, he put the hot ice cream mix into his freezer. He was surprised that his ice cream froze faster than the colder mix of his fellow students. Mpemba’s teacher and classmates laughed at his claim that the hot mix froze faster.

Later, a noted British physicist named Denis Osborne came to the African school, and Mpemba asked him to explain why hot water freezes faster than cold. Not only did his teacher and classmates think Mpemba’s suggestion was absurd, but the physicist was also skeptical. However, Dr. Osborne was open-minded enough to test it experimentally. (Like I suggested to my father and aunt.) In 1969, when Mpemba was in college, he and Osborne published a paper on the phenomenon, which came to be called the Mpemba effect.

So some people, when asked, “Does hot or cold water freeze faster?” were no longer laughing at the “foolish question.” However, nobody knew how hot water could freeze faster. After all, if the water is already closer to freezing temperature, it should freeze in less time. Shouldn’t it? The truth is that the question does not have a simple answer. In 2013, scientists in Singapore proposed a solution. Tomorrow, we will look at their explanation.

— Roland Earnst © 2023