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Dry ice has the unique ability to both keep food fresh when shipped over long distances and create a dramatic scene at a party. However, if this form of ice behaves so differently than regular ice, does it go through the same evaporation process?
Dry ice does not evaporate, as evaporation is a process in which liquids become gases. Since dry ice is frozen carbon dioxide, when it breaks down and becomes a gas, the process is called sublimation. While they are similar, sublimation is the correct term to use.
The rest of this article will dive deeper into the sublimation process and its difference from evaporation, dry ice versus regular ice, and proper handling of dry ice.
Why Dry Ice Doesn’t Evaporate
It makes sense to assume that dry ice evaporates. Most of us are familiar with the process of evaporation and witness it on a fairly regular basis, like noticing how a puddle dries up once the sun rises.
It’s a much more common process than sublimation, with the US Geological Survey stating that sublimation accounts for a very small amount of water vapor entering the atmosphere.
Even though dry ice and regular ice look similar and are both used for cooling purposes, they’re different in many crucial ways.
Let’s take a closer look at some of these differences to understand why these similar substances become gasses in such different ways.
Differences Between Dry Ice and Normal Ice
The main difference between dry ice and regular ice is that dry ice is made of frozen carbon dioxide, while anyone can make regular ice at home by simply bringing water to its freezing point (32°F/0°C).
According to Continental Carbonic, making dry ice is a complicated process that involves pressurized containers and other special equipment.
Other significant differences between dry ice and regular ice include:
- Regular ice is safe to put in beverages, but dry ice can be life-threatening if consumed.
- Dry ice is significantly colder than regular ice, with UC Santa Barbara scientists estimating an average temperature of -80°C (-176°F). This lower temperature means that it stays cold longer.
- Dry ice is roughly twice as heavy as regular ice.
Evaporation vs. Sublimation
One of the major differences between dry ice and regular ice is how they break down or change from their solid form.
Evaporation and sublimation are very similar, with both processes ending with the creation of gas. Evaporation, however, is the process of a liquid changing into gas, while sublimation is the process of a solid turning to gas.
While there are many examples of evaporation in play all around us on a daily basis, it is fairly difficult to see sublimation in action.
Watching smoke come off of dry ice is definitely the easiest example, but since many of us don’t interact with dry ice on a daily basis, this isn’t always convenient. Check out this YouTube video to see sublimation in action:
Another example of sublimation that we are all likely familiar with is freezer burnt meat. As Discover Magazine explains, freezer burn occurs when ice particles on frozen meat sublimate, leaving behind tiny holes.
These holes increase the surface area of the meat, leaving more tissue exposed to the air. It then speeds up fat oxidation in the meat and gives it a rancid, “old” taste.
It’s also worth noting that carbon dioxide only exists in gas and solid form at room temperature and a normal pressure – hence the sublimation.
While it is possible to produce liquid carbon dioxide under the right conditions, it’s nearly impossible for it to happen to the average person just trying to cool food and drinks.
This makes dry ice perfect for packing ice chests for long journeys, as nothing inside will get wet or soggy.
What Causes Sublimation?
Think of sublimation as dry ice “melting.” Just as with regular ice, if exposed to heat, dry ice will eventually reach a certain temperature at which it will change its state.
This temperature is around -78.5°C(-109.3°F), according to the US Geological Survey. At this temperature, you’ll be able to see smoke coming off of the ice. This smoke is a mix of cold, humid air, and carbon dioxide gas.
Although it might not be easy for most of us to access, the peaks of Mt. Everest is a great place to see sublimation happening in nature. With low air pressure, freezing temperatures, and lots of direct sunlight, the conditions are perfect for sublimation.
How Long Does Dry Ice Take to Sublimate?
Dry ice sublimates fairly quickly, as anywhere it is stored will likely be a lot warmer than the ice itself. Accordingly, it’s best to pick up your ice as close to when you will need it as possible so as not to waste any. Florida International University suggests that since dry ice sublimates at 10%, you can expect to lose between 5 and 10 pounds of ice every 24 hours.
You can further slow down sublimation by taking a few additional steps:
- Pack the dry ice in a heavily insulated cooler.
- Minimize air pockets in the cooler by packing contents tightly and filling extra space with regular ice.
- Wrap dry ice in multiple sheets of newspaper or towels.
- Place dry ice at the top of the cooler, not the bottom.
Dry Ice Safety and Handling Tips
Along with the many benefits of using such cold, long-lasting ice, there are risks associated with handling dry ice. Mishandling can lead to serious injuries, but taking a few additional precautions can make any experience with dry ice a positive one.
Keep Dry Ice Away From Bare Skin
Since dry ice is so cold, touching it with your bare hands can cause extreme frostbite. Make sure to always use tongs or thick, insulated gloves while handling. These soft Cryogenic Gloves from Amazon can withstand dry ice temperatures and can cover all the way up to your shoulder. If you plan on breaking up or cutting the ice, you’ll also want to invest in a pair of goggles.
Don’t Use Airtight Containers
Even though using an insulated cooler can help extend the life of dry ice, it’s not a good idea to make the container airtight. As the ice sublimates and carbon dioxide builds up, the pressure from the gas could cause the cooler to burst, which can be dangerous. I recommend the Yeti Tundra 65, which is durable enough to handle dry ice and can be easily ventilated for safety.
The National Weather Service also recommends cracking a window if you’re traveling with a cooler full of dry ice. This prevents too much carbon dioxide from building up around you, which can be incredibly dangerous. This applies even if the cooler is in the trunk, as air circulates throughout the entire vehicle.
Never throw dry ice away or leave in your sink to sublimate. While the ice is unlikely to damage anything, it still poses a safety risk to anyone that unknowingly touches it. Instead, place unused ice in a well-ventilated container and place outside. Make sure it’s out of reach of children and pets to ensure that no one is injured.
Dry ice becomes a gas differently than regular ice because it is made of entirely different elements. We can thank the sublimation process for not only the fantastic fog that dry ice is known for but also for its many other wonderful properties. With a couple of extra safety measures, dry ice can be incredibly useful in setting a scene and keeping things fresh.