Erasto Mpemba asked the question "If you take two similar containers with equal volumes of water, one at 35 °C (95 °F) and the other at 100 °C (212 °F), and put them into a freezer, the one that started at 100 °C (212 °F) freezes first. Why?" (1963)
The answer is very simple and basic.
Hot water molecules are moving faster than cold water. Because their gained energy for move and vibration are higher. Entrophy is high.
As a second, all water molecules are moving to strike each other according to their contained energy.
In cold water, all molecules have got nearly same level energy, so by cooling they will act nearly same. When striking molecules to each other there is less consumption in energy level. Because all the water molecules are nearly homogeneous and in balance. Entrophy is low.
On the contrary, medium (celcius) degree of hot water molecules even decrease to the same level degree of cold water, hot water molecules are acting different. Because their entrophies are still very different.
In the cup of hot water, there are some different regions where contain some more hot and some more cold molecules. Also there is no balance in hot water regions because of convective flows.
Like billiard balls in pool, hot water molecules are hitting to each other. And sometimes the hit the molecules of colder zones molecules. By hitting they lost their energy. Of course by cooling, cold water molecules are loosing energy in the same way. But they can maintain balance between them.
However hot water molecules are faster and causing more collision. Also energy absorption level is higher (than cold water) because of hitting from different directions. Sometimes directly toward each other, sometimes with angles. So there is no balance between some core cold zones and some hot zones. There is no harmony in cooling hot water. Even molecules behave differently. High entrophy in cooling hot water causes loosing energy while entrophy is going to low.
In cold water harmony, loosing energy level is slowly. Because when a molecule lost its energy, the other molecule(s) is/are gained energy which some of it used for movement and for transferring to a new molecule with vibration.
Same reason is also causing boiling water after heating by micro vave. When you heat by microwave, there is no boiling until you blend with a spoon or pouring into a cup, altough the temperature is higher than 100 Celcius . With blending or pouring, molecules are starting to hit each other. So every molecules gives back the stored energy by hitting to each other, because of the fact that balance was broken.
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