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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