Question
Sat April 04, 2015 By: Vishwaketu Malakar

Why hot water freeze faster than the normal water? please give me a complete answer for this reason?
 

Expert Reply
Prachi Sawant
Sun April 05, 2015

In water molecule, two hydrogen bonds are covalently bonded to each other. Also, two molecules of water are also bonded to each other by weak hydrogen bonding. It happens when hydrogen atoms of one water molecule sits close to oxygen atom of another water molecule. Covalent bonds get stretched and store energy due to natural repulsion when two water molecules come closer. On heating, hydrogen bonds get stretched  and  water get less dense. This extra stretch in hydrogen bonding relax covalent bonds which releases stored energy. This process of covalent giving up energy is equivalent to cooling. Hence warm water freezes faster than normal cold water.

This effect is called Mpemba effect.

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