How Cold Is Liquid Nitrogen?

Cannister of liquid nitrogen

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Liquid nitrogen is very cold! At normal atmospheric pressure, nitrogen is a liquid between 63 K and 77.2 K (-346°F and -320.44°F). Over this temperature range, liquid nitrogen looks much like boiling water. Below 63 K, it freezes into solid nitrogen. Because liquid nitrogen in a usual setting is boiling, its usual temperature is 77 K.

Liquid nitrogen boils into nitrogen vapor at room temperature and pressure. The cloud of vapor that you see isn't steam or smoke. Steam is invisible water vapor, while smoke is a product of combustion. The cloud is water that has condensed out of the air from exposure to the cold temperature around the nitrogen. Cold air cannot hold as much humidity as warmer air, so a cloud forms.

Being Safe With Liquid Nitrogen

Liquid nitrogen is not toxic, but it does present some hazards. First, as the liquid changes phase into a gas, the concentration of nitrogen in the immediate area increases. The concentration of other gases decreases, particularly near the floor, since cold gases are heavier than warmer gases and sink. An example of where this can present a problem is when liquid nitrogen is used to create a fog effect for a pool party. If only a small amount of liquid nitrogen is used, the temperature of the pool is unaffected and the excess nitrogen is blown away by a breeze. If a large amount of liquid nitrogen is used, the concentration of oxygen at the surface of the pool might be reduced to the point where it can cause breathing problems or hypoxia.

Another hazard of liquid nitrogen is that the liquid expands to 174.6 times its original volume when it becomes a gas. Then, the gas expands another 3.7 times as it warms to room temperature. The total increase in volume is 645.3 times, which means vaporizing nitrogen exerts immense pressure on its surroundings. Liquid nitrogen should never be stored in a sealed container because it could burst.

Finally, because liquid nitrogen is so very cold, it presents an immediate danger to living tissue. The liquid vaporizes so quickly a small amount will bounce off the skin on a cushion of nitrogen gas, but a large volume can cause frostbite.

Cool Liquid Nitrogen Uses

The quick vaporization of nitrogen means all of the element boils off when you make liquid nitrogen ice cream. The liquid nitrogen makes the ice cream cold enough to turn into a solid, but it doesn't actually remain as an ingredient.

Another cool effect of the vaporization is that liquid nitrogen (and other cryogenic liquids) appear to levitate. This is due to the Leidenfrost effect, which is when a liquid boils so rapidly, it's surrounded by a cushion of gas. Liquid nitrogen splashed onto the floor appears to skitter away just over the surface. There are videos where people throw liquid nitrogen out onto a crowd. No one is harmed because the Leidenfrost effect prevents any of the super-cold liquid from touching them.

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Helmenstine, Anne Marie, Ph.D. "How Cold Is Liquid Nitrogen?" ThoughtCo, Apr. 5, 2023, Helmenstine, Anne Marie, Ph.D. (2023, April 5). How Cold Is Liquid Nitrogen? Retrieved from Helmenstine, Anne Marie, Ph.D. "How Cold Is Liquid Nitrogen?" ThoughtCo. (accessed June 7, 2023).