When we put cold water in the fridge it takes time to freeze but hot water is fast in freezing.Why?


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This phenomenon is called the mpempa effect. There is a research paper which explains this using hydrogen bonding The paper is slightly difficult to understand which can be found here

This is a simpler version which I found here

Now Xi and co say hydrogen bonds also explain the Mpemba effect. Their key idea is that hydrogen bonds bring water molecules into close contact and when this happens the natural repulsion between the molecules causes the covalent $\ce{O-H}$ bonds to stretch and store energy.

But as the liquid warms up, it forces the hydrogen bonds to stretch and the water molecules sit further apart. This allows the covalent molecules to shrink again and give up their energy. The important point is that this process in which the covalent bonds give up energy is equivalent to cooling.


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