Friday 31 October, 2014

Freezing point of water pegged at minus 55F

Published On: Thu, Nov 24th, 2011 | Chemistry | By BioNews

The lowest temperature liquid water can reach before it becomes ice is -55 degrees Fahrenheit, a new study has suggested.

The temperature is 87 degrees Fahrenheit colder than what most people consider the freezing point of water, namely, 32 F.

According to the new study by chemists Valeria Molinero and Emily Moore,
supercooled liquid water must become ice at minus 55 F not just because of the extreme cold, but because the molecular structure of water changes physically to form tetrahedron shapes, with each water molecule loosely bonded to four others.

The findings suggest that this structural change from liquid to “intermediate ice” explains the mystery of “what determines the temperature at which water is going to freeze,” said Molinero, an assistant professor at the University of Utah and senior author of the study.

“We’re solving a very old puzzle of what is going on in deeply supercooled water.”

How and at what temperature water must freeze has more than just ‘gee-whiz’ appeal. Atmospheric scientists studying global warming want to know at what temperatures and rates water freezes and crystallizes into ice.

“You need that to predict how much water in the atmosphere is in the liquid state or crystal state, which relates to how much solar radiation is absorbed by atmospheric water and ice,” Molinero said.

“This is important for predictions of global climate,” he added.

Molinero and Moore devised a new computer model that is 200 times faster than its predecessors.

The model simplified the number crunching by considering each three-atom water molecule to be a single particle similar to a silicon atom and capable of sticking together with hydrogen bonding.

The study has been recently published in the journal Nature.

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