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Why does hot water freeze faster than cold water?

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Why does hot water freeze faster than cold water?

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Published by University of Leicester Press Office for University of Leicester in Education and also in Communities

University of Leicester student selected as finalist from among 22,000 entries

A University of Leicester student is a finalist in a worldwide competition to find the best answer to the question: Why does hot water freeze faster than cold water?

The competition was set in June 2012 by the Royal Society of Chemistry  which sought an answer to this question. The idea was to allow the public to submit an answer within four weeks of issuing a call for explanations, regardless of format or scientific training. Anyone could answer using any online media from anywhere in the world. The response was overwhelming with more than 22,000 entries from as far afield as Bolivia, Australia and Uzbekistan

Now second year Chemistry student Adam Smith, from Kettering in Northamptonshire, is among the final 11 shortlisted finalists. He entered the competition as part of a summer project he was doing in the Department of Chemistry working with Dr Adrian Boatwright, Dr Shengfu Yang, and Professor Andrew Ellis.

Dr Boatwright said: “When we started we had no idea if the effect was genuine so it was a great surprise when we actually saw the hot water freeze first. Adam is a great student and it was fun helping him solve this problem.”

Adam added:  ''The number of entries to the competition was surprising; it just shows how much interest the world has in science. The effect was very interesting to investigate and I am sure it will continue to fascinate scientists across the world until a more solid proof can be found.''

At first sight the question  "Does hot water freeze faster than cold?"  would seem to be a ridiculous one – almost everyone would expect cold water to freeze faster.

However, some 40 years ago an African boy called Erasto Mpemba  noticed that ice cream would often freeze faster when cooled from a high starting temperature rather than letting the mixture cool to ambient temperature. Mentioning this effect to his teacher, he was immediately mocked for the ridiculousness of such an observation and that he should move on to more scientific studies. However the boy did not accept the rebuff and with persistence managed to persuade the teacher to do the science, only this time with water. The effect, now called the Mpemba effect, turned out to be real. This exposed what was thought to be a serious flaw, or so it was thought, in our understanding of the thermal properties of water.

The Final winner will be announced at The Chemistry Centre at the Royal Society of Chemistry in London on the 10th of January 2013 and the twenty finalists have been invited to this award ceremony.

For more information

http://www.rsc.org/mpemba-competition/

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