Liquid nitrogen boils at -196°C
To be accurate, its boiling point is −195.79 °C (−320 °F, 77K). The ‘K’ there stands for Kelvin. This is a temperature scale used by scientists whereby the lowest point, zero, is called absolute zero. At absolute zero all thermal motion stops. Getting back to a more familiar scale, if nitrogen’s boiling point is −195.79 °C (−320 °F), then it means it is a liquid only at very, very low temperatures.
Even though nitrogen is non-toxic, odourless, colourless, relatively inert and is not flammable, it is certainly not without its hazards:
1. Because it is so cold when in a liquid state, if you touched it, your skin and general living tissue would rapidly freeze, resulting in frostbite. Because of this ability to rapidly freeze living tissue, it is known as a cryogenic fluid.
2. When liquid nitrogen boils (or transitions from a liquid into a gas), it expands into a gas that is 174.6 times bigger than the original volume of the liquid. As it warms up to room temperature it expands another 3.7 times. This gives a total expansion of 645.3 times the original volume of the liquid. So if you store liquid nitrogen in a sealed container, it will burst. Or explode.
3. Finally, be careful if you’re thinking of using liquid nitrogen for an atmospheric fog effect at your pool party. As Anne Marie Helmenstine, Ph.D, helpfully points out, “…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.” So maybe make do with some lovely poolside cocktails instead.
But it’s not all doom and gloom, as Anne Marie Helmenstine, Ph.D also illustrates, “…liquid nitrogen (and other cryogenic liquids) appears to levitate. When a liquid boils so rapidly, it’s surrounded by a cushion of gas. [So when] liquid nitrogen [is] splashed onto the floor [it] appears to skitter away just over the surface.”
By Graham Foster
Graham is a graphic designer with a passion for science
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