I heard about this thing called the Mpemba effect where hot water can freeze quicker than cold water under certain conditions. How does that even work?
In: Chemistry
To start with there is still ongoing debate about if it is even a thing. – [source](https://arxiv.org/abs/2010.07287) Taken from the Wikipedia article on the topic.
That out of the way, the [Wikipedia article on the effect](https://en.wikipedia.org/wiki/Mpemba_effect#Suggested_explanations) has a section covering possible explanations. It is one of those things where it’s unclear if it’s a real effect, and thus there are no real answers. Mainly because there hasn’t been exhaustive research into it.
The Mpemba effect, where hot water freezes faster than cold water under certain conditions, is thought to happen for a few reasons. One theory is that hot water evaporates faster, reducing the volume of water that needs to freeze. Another idea is that the temperature difference between hot water and the freezing environment can increase the rate of cooling. Also, hot water can lose its gas content more quickly, leading to a change in its properties that might affect freezing times. The exact cause is still a topic of research, but these factors contribute to the curious phenomenon.
It doesn’t. Given identical environnement, the water that starts at a lower temperature will reach freezing temp first
spraying hot water as tiny droplets immediately freezes into floating ice-crystals, because heat from the hot-water dissipates quicker into the atmosphere.
I still remember this being a question asked in a science class in HS in the 90s and finding out many years later that we still don’t know
The real answer is transitional energy. Water doesn’t actually freeze at 32°F, it STAYS frozen at 32. You need to cool it slightly below 32 to initialize the crystalization. This is the transitional energy. You also need impurities in the water but that’s an answer to a different question.
Hot water is less dense than cold water so it loses its heat proportionally faster. So when hot water reaches freezing temperature it has more momentum when it hits a point where the transition to a crystal would stall briefly were you to have started with colder water.
Alright, so here’s the deal with the Mpemba effect, where hot water sometimes freezes faster than cold water. It’s kind of weird, right? Well, scientists think it has to do with how the water molecules behave when they’re heated up.
When you heat water, the molecules start moving around faster, which can mess with the way ice crystals form when it starts to freeze. So, even though hot water might seem like it’s further from freezing, it might have fewer impurities or spots where ice crystals can start forming.
Plus, hot water cools down faster because it can lose more water vapor to the air as it evaporates. And the way hot water moves around in the container can help it cool more which might speed up the freezing process.
But here’s the kicker, the Mpemba effect doesn’t always happen, and it can depend on a bunch of different factors like the temperature of the water, the container it’s in, and even the air around it. Scientists are still trying to figure out all the details, but for now, it’s just one of those cool mysteries of science!
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