Researchers claim to have solved the Mpemba effect - why warm water freezes faster than cooler water | Teacher Tools and Tips | Scoop.it

team of researchers at Singapore's Nanyang Technological University believes they have solved the mystery of why warm water freezes faster than cooler water. It has to do with the way energy is stored in the hydrogen bonds between water molecules they suggest in their paper which they've uploaded to the preprint server arXiv.

The researchers demonstrate that the Mpemba paradox arises intrinsically from the release rate of energy initially stored in the covalent H-O part of the O:H-O bond in water albeit experimental conditions. Generally, heating raises the energy of a substance by lengthening and softening all bonds involved. However, the O:H nonbond in water follows actively the general rule of thermal expansion and drives the H-O covalent bond to relax oppositely in length and energy because of the inter-electron-electron pair coupling [J Phys Chem Lett 4, 2565 (2013); ibid 4, 3238 (2013)].

 

Heating stores energy into the H-O bond by shortening and stiffening it. Cooling the water as the source in a refrigerator as a drain, the H-O bond releases its energy at a rate that depends exponentially on the initially storage of energy, and therefore, Mpemba effect happens.

 

This effect is formulated in terms of the relaxation time tau to represent all possible processes of energy loss. Consistency between predictions and measurements revealed that the tau drops exponentially intrinsically with the initial temperature of the water being cooled.


Via Dr. Stefan Gruenwald