A Guide to the Chemistry of Cold Weather

Frozen Chicago
Photo: AP

You might have noticed that it’s pretty cold throughout much of the United States—frostbite-inducing, school-closing, scald-yourself-with-boiling-water-while-attempting-that-stupid-instant-snow-trick cold. You might wonder what that means, scientifically.

I’m not talking biology—I’m talking chemistry (okay, and a little biochemistry). Temperatures like the -36 degrees Fahrenheit faced by my friends in Fargo, North Dakota this week approach a level of frigid that can alter the very nature of the matter around us.

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“Chemistry happens quite differently [in the cold],” Henry Rzepa, computational chemist at Imperial College London, told Gizmodo.

First, the basics: Temperature is the average kinetic energy of the molecules in a given substance; or basically, how much the atoms jostle around. Chemistry is the study of how these atoms interact with one another, forming and breaking bonds or reacting to create new substances under the influence of energy, temperature, and pressure.

The most obvious affect of lower temperatures on molecules is that they can cause substances to go through phase transitions, meaning changing their characteristic nature from gas to liquid or liquid to solid.

In the lower-temperature regime called “outside my partner’s parents’ house near Grand Forks, North Dakota,” air molecules begin to move slower, exerting less pressure on surfaces and causing car tire pressures to decrease. Water freezes and the air can’t hold as much water vapor. That’s how that boiling water trick works—water droplets vaporize from the heat, but the air’s too cold to hold any more water vapor, so the droplets quickly freeze out.

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Chlorine gas becomes a liquid at -30 Fahrenheit (-34 Celsius). Propane gas is a liquid at -44 Fahrenheit (-42 Celsius), and gasoline, actually a mixture of different carbon-based molecules, could freeze at around -40 degrees Fahrenheit and Celsius. The U.S. Armed Forces required certain liquid propellants to function down to -65 Fahrenheit for certain missiles, Jon Austad from the Hylleras Center for Quantum Molecular Sciences and Kathrin Hopmann from the Arctic University of Norway explained to Gizmodo via email: “As a consequence, certain surface-to-air missiles, JATOs etc., may not work at low temperature.”

Then there’s an even weirder phenomenon, called tin pest phenomenon; below 56 degrees Fahrenheit (13 degrees Celsius), tin transforms from a metal into a brittle, non-metallic form. It’s a slow process at higher temperatures but occurs much quicker around -22 Fahrenheit (-30 Celsius). “This has been ascribed as one of the reasons [Robert Falcon Scott’s] expedition to Antarctica failed,” said Hopmann and Austad. The tin containers filled with kerosene that Scott’s team had stashed away turned out to be empty—possibly because tin pest created leaks in the cans.

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But there’s more to chemistry than states of matter. Higher temperatures typically lead to more higher-energy collisions between faster-moving molecules, and thus would lead to faster chemical reactions. So lower temperatures would, therefore, slow down chemical reactions.

Chemical reactions you rely on daily begin to putter out in these temperatures. Most noticeably, your phone dies. The low temperatures make lithium ions move more slowly between the electrodes of lithium-ion batteries, Xiao Ji, postdoctoral research associate at the University of Maryland, explained to Gizmodo. But of more worry is the electrolyte that the molecules travel through, which solidifies at these low temperatures. Ji’s team is working on better electrolytes to combat that problem.

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But even -36 degrees Fahrenheit isn’t all that cold from a chemistry standpoint, explained Rzepa. In many of the labs in the Imperial College chemistry department, researchers are more interested in the -109.2 Fahrenheit, (-78.5 Celsius) kind of cold, the temperature at which carbon dioxide freezes. That’s more of a convenience thing, since at that temperature, reactions too quick to study at room temperature become controllable in the lab.

Are there other experiments that, in -36 degree Fahrenheit cold, one could just perform with the lab’s windows open to save on energy costs? In fact, there are—one holy grail of physics is the room-temperature superconductor. Some materials at low temperatures undergo another kind of phase transition such that electrons move without any electrical resistance. If room-temperature superconductors were realized, they could drastically reduce energy costs or help other technologies, like quantum computers, become more feasible. One recent result shows that a material called lanthanum hydride could become a superconductor at around -10 Fahrenheit (-23 Celsius). But there’s a catch: the phase transition only occurs at extreme pressures, around half the pressure experienced at the center of the Earth.

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Ultimately, the most important chemical reactions to our livelihood, the ones occurring in our own bodies, are the ones that we should be most worried about. Indeed, one researcher wrote a paper on the temperature limits of Earth’s life. Chemical reactions inside cells function at optimal temperatures, and lower temperatures can cause disruption. We eat food in order to power those reactions and keep our body warm, but without a coat, we would quickly succumb to the effects of cold.

Typically, organisms have a temperature at which they can survive, and another at which they can actually undergo processes like reproduction and digestion. Vertebrates are relatively wimpy and have evolved things like fur and feathers (and the ability to construct heated buildings and sew clothing) in order to keep their cells operating at optimal warm temperatures. Marine life can only handle the coldest temperature at which water exists as a liquid, 32 Fahrenheit for freshwater and 28 Fahrenheit for seawater. Older data suggests that flowering plants can survive down to -94 Fahrenheit (-70 Celsius), but can only thrive at around 32 Fahrenheit (0 Celsius). At temperatures below -4 Fahrenheit (-20 Celsius), bacteria can still multiply, albeit more slowly, according to one study, perhaps thriving on saline meltwater puddles. Bacteria and archaea, and even the microscopic animals called tardigrades, can survive reanimation after freezing to temperatures below -320 Fahrenheit (-196 Celsius), though tardigrades still require at least 32 degree Fahrenheit temperatures to thrive.

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That’s just Earth, chemist Kamila Muchowska at the University of Strasbourg in France explained to Gizmodo. It’s interesting to think about these extremes of bodily chemistry to better understand whether life could exist elsewhere—places where water might remain a liquid at colder temperatures thanks to the presence of salts.

Anyway, -40 is cold extremely cold for us humans, but from a chemistry standpoint, it rates as merely brisk.

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About the author

Ryan F. Mandelbaum

Science writer at Gizmodo | I like physics and eating