When hot and cold water are put into the fridge at the same time, the hot water freezes first, which is counter-intuitive but true

When I went to my little cousin's house the other day, I happened to run into his mother and asked him to help me freeze the ice water. Then this little guy picked up the hot water he had just boiled, filled a glass, and put it in the fridge. When his mother saw this, she hurriedly took the hot water out and then criticized and taught him. Looking at his aggrieved face, I couldn't help but want to take revenge for him.

From the point of view of getting ice water faster, the young cousin did the right thing. But from the point of view of protecting the fridge, indeed, you can't put hot water in it. This is because the fridge will warp, the foaming agent will expand, the life of the compressor will be shortened, electricity consumption will increase and the temperature inside the fridge will rise, causing other items to warm up and deteriorate, and the walls of the fridge will tend to freeze with water vapor. In fact, my little cousin is still young and doesn't know anything and won't be criticized and educated. So I did it anyway. Eventually, he learned to care for the fridge, and through me, he understood that his actions were not wrong.

Having said that, I'm sure many of you are thinking, or probably thinking, that I misrepresented the facts for the sake of a child. Common sense dictates that to get ice water, it must be cooled down with cold water. It must take longer to cool down with hot water. After all, it takes a certain amount of time for hot water to cool down to cold, and the same amount of time to cool down to ice water at a later stage.

Yes, this is the result of our habitual thinking. But not all reality is the same as the reasoned conclusion. The laws of the world are sometimes strange. Let me give you an example. When we take something out of the fridge to defrost it, what kind of water do we choose? Most people just use a jug of hot water. But actually, the fastest way is to put it under the tap and rinse it with tap water.

The reason for hot water freezing faster is the mpemba effect. The phenomenon was discovered because of a child called Mpamba. At the time he was a secondary school student in the East African country of Tanzania. They were allowed to make ice cream at school. To have somewhere to freeze their own ice cream, he always added sugar to the hot milk and then immediately put it in the freezer. Later, he found that his ice cream froze the fastest. A few years later, in collaboration with Dr. Dennis Osbourne, he published a paper on this phenomenon, which he called the mamba effect.

However, the paper has been questioned, dismissed as a joke, and even appeared in the Top Ten Scientific Deceptions of the 20th Century, where it was widely circulated and quoted to refute the rumors. But anyone who has done the experiments in question knows that it is true that hot water freezes first. So people just extrapolate from common sense as their main basis, rather than refute it with the truth that comes from the experiment. This is why so many eye-catching articles and videos nowadays earn traffic and mislead people.

The Mpemba effect is that the molecules of a slightly warmer liquid in direct contact with the cooling environment will fall faster than those of a slightly cooler temperature for the same mass and the same cooling environment. If the cooling environment can always be kept at the same cooling capacity (constant temperature), the higher temperature liquid will fall to the cooling environment temperature first; if the temperature is below the freezing point of the liquid, the higher temperature liquid will freeze first.

Although it illustrates what this phenomenon looks like, the ultimate principle is still not an accurate statement. the Mpemba effect may be due to the freezing point. As we said before, there are impurities in the water and the freezing point will be different. Another theory is that water at lower temperatures is supercooled, not frozen and that the enhanced convection in water at higher temperatures accelerates cooling by maintaining a thermal gradient across the walls of the vessel. Another theory is that as the temperature increases, the overall hydrogen bonding weakens, where weak electrostatic hydrogen bonds break and the number of strong hydrogen bonds increases; as the warm water cools rapidly, the presence of small, strongly bound clusters caused by these small amounts of strong hydrogen bonds promotes the nucleation of hexagonal ice.

Opinions vary and each has its possibilities, but so far there is no definitive answer. After all, something so counterintuitive will not be accepted without an accurate statement (although many things are not necessarily accepted by the general public even when stated). So let's put it aside for now. We know the phenomenon, so let's learn it!

I think it's a summary of the main points :

1. The mpemba effect is that the molecules of a slightly warmer liquid in direct contact with the cooling environment will fall faster than those of a slightly cooler temperature, given the same mass and the same cooling environment. If the cooling environment can always maintain the same cooling capacity (constant temperature), the higher temperature liquid falls to the cooling environment temperature first, and the temperature below the freezing point of the liquid, the higher temperature liquid freezes first.

2. This phenomenon was discovered because of a child called Mpamba. At the time he was a secondary school student in the East African country of Tanzania. They were allowed to make ice cream at school. To have somewhere to freeze their ice cream, he always added sugar to the hot milk and then immediately put it in the freezer. Later, he found that his ice cream froze the fastest. A few years later, in collaboration with Dr. Dennis Osbourne, he published a paper on this phenomenon and called it the mpemba effect.

3. The mpemba effect may be due to the freezing point. We said before that the freezing point would be different with impurities in the water. Another theory is that water at lower temperatures is supercooled, rather than frozen, and that the enhanced convection in water at higher temperatures accelerates cooling by maintaining a thermal gradient across the walls of the vessel. Another theory is that as the temperature increases, the overall hydrogen bonding weakens, where weak electrostatic hydrogen bonds break and the number of strong hydrogen bonds increases; as the warm water cools rapidly, the presence of small, strongly bound clusters caused by these small amounts of strong hydrogen bonds promotes the nucleation of hexagonal ice.