I remember sitting in elementary school science class while a special guest demonstrated the “magic” of dry ice, I was captivated. We, the students, were sitting much further away from the demonstration table than usual, understanding that dry ice could be very dangerous. I’m sure this special guest conveyed several wonderful tidbits about the science behind dry ice—but at that age, let’s face it, explanations went in one ear and out the next because we were so riveted on the visuals—ice that didn’t get wet, let alone melt in water, the bubbling and steam. It was the best magic show we’ve ever seen.
I thought back on all this the other day while, of all things, while I was watching a cooking channel. In a race to beat her opponents by creating an award-winning dessert in under 30 minutes, this chef perfected her double-rich molten cake by topping it with raspberry ice cream she made using dry ice in under 45 seconds. It occurred to me that, as a scientist and a Water Street blogger, I could enlighten all those adults with the dry-ice science they missed as goggled-eyed kids. So, here goes!
Of all the fascinating attributes of dry ice, there are just two I’ll touch on today. The first, unlike the ice we typically think of, there is no water in dry ice, it is made up of frozen carbon dioxide. Dry ice gets its name because it never enters a water state—instead when the solid carbon dioxide is heated, it goes directly into a gaseous state, skipping the liquid state completely, or in scientific terms, undergoing sublimation. As you can imagine, with a surface temperature of negative 109.3 degrees, it doesn’t take much to start the sublimation process here on earth—any environment warmer than -109.3F will do! So, as soon as dry ice starts to “melt” it turns directly into carbon dioxide gas and is released into the atmosphere.
That brings me to point number two in this dry ice lesson. If you’re suddenly feeling guilty for enjoying the visual beauty of melting dry ice because of all our discussions linking increased carbon dioxide emissions to global warming and other environmental problems like higher acidity of ocean waters—rest easy. Dry ice is very environmentally friendly. In a way, dry ice sublimation is a “zero sum game”. Although dry ice is made from solid carbon dioxide, it never produces or releases excesses carbon dioxide into the environment when it turns into its gaseous form and does not contribute to the greenhouse effect.
In fact, dry ice is being used more in more as replacement “technology” for more environmentally destructive processes. Dry ice blasting, which replaces chemical cleaning solvents with dry ice pellets to safely clean all types of industrial equipment, is a great example. Agriculture, meat processing, food and fuel shipping, pest control, emergency preparedness—the list of industries tapping into eco-friendly dry ice alternatives to improve their processes goes on and on.
So, while the “magic display” of dry ice may not get us quite as excited as adults as it did when we were kids, we can get excited about the very real scientific properties that give dry ice tremendous potential for contributing to the sustainability and well being of our planet.
