Tag Archives: Dry Ice

The Coolest Molecules

CAUTION: This experiment uses dry ice (-109˚F) and liquid nitrogen (-321˚F). Proper safety equipment should always be used when handling these substances.

Physics tells us that pressure, volume and temperature are all linked when talking about gases. So what does this have to do with solid carbon dioxide (dry ice) and liquid nitrogen? When dry ice is placed into a balloon at room temperature, which is then tied off, it will start to warm up.

molecules

Since the ambient air temperature is roughly 65˚F, the air that surrounds the balloon is more than 150 degrees warmer than the dry ice! This hug difference adds energy to the dry ice turning it into gaseous carbon dioxide through the process of sublimation. Sublimation is the phase transition of a substance directly from the solid to the gas phase without passing through the intermediate liquid phase.

molecules cool

Now that there is a balloon full of carbon dioxide gas we can cool it down with something colder than dry ice. This is where liquid nitrogen comes in. The balloon gets dunked into a bowl full of the -321˚F liquid! Cooling the gas in the balloon down means that it loses energy making the molecules start to clump, making the balloon lose volume. It will turn the carbon dioxide gas back into a solid through the process of deposition. Deposition is basically the opposite of sublimation, turning the gas directly into a solid.

molecules done

This process of cooling and warming to change the balloon’s volume can be repeated over and over again. Or, with the inflated balloon, dunk it in the bowl of liquid nitrogen, take it out, and before it can expand again, rip it open to see the solid carbon dioxide for yourself!

Written By: Mimi Garai

 

How Do You Melt Dry Ice?

Dry ice is the solid state of carbon dioxide, the gas we all breathe out, but have you ever seen it in liquid form? When left at room temperature, dry ice doesn’t actually melt; it sublimates, changing directly from a solid to a gas. To understand why, let’s take a look at its phase diagram, a plot of the states of CO2 relative to temperature and pressure.

At standard pressure of one atmosphere, liquid CO2 is unsustainable and any solid carbon dioxide above -109℉, or -78℃, directly converts to a gas. In order for liquid CO2 to exist, the pressure needs to be increased to at least 5.11 atmospheres; which is where our pressure syringe comes in.

Substances tend to condense as pressure increases, changing down in state from gas to liquid or liquid to solid or at least making that state change easier. As the plunger of the pressure syringe drops, the pressure increases to the point where dry ice melts rather than sublimating and CO2 can be held in liquid form.

Just as increasing pressure aids substances in changing down in state, decreasing pressure facilitates changing up in state. At sea level, the boiling point of water is 212 degrees Fahrenheit, but if you live at 5500 feet like those of us at AstroCamp, that boiling point is decreased to 201.5 degrees. This 10.5 degree difference may not seem significant, but that’s the result of a change of less than 0.2 atm. In a vacuum chamber, water will actually boil at room temperature because of the immense drop in pressure.

 

Into Thin Air: CO2 Science

Carbon dioxide, or CO2, is one of the handful of compounds that most people are familiar with. People and animals breathe it out, plants love it, and we make a lot of it, which probably has some consequences. We are going to look at this well known gas in its solid form and hopefully answer any questions that come up along the way!

bigbubbs croppedSolid carbon dioxide is more often referred to by the name dry ice. This is because it never leaves behind a wet spot when it disappears. Unlike water, which will melt to a liquid naturally under normal conditions at room temperature, dry ice will instead skip to a gas. To the left, you can see dry ice under water releasing bubble after bubble of transparent carbon dioxide gas. This physical transition from a solid to a gas is called sublimation, and isn’t anything to be afraid of. Its just the less familiar cousin of evaporation and condensation. For more on that, check out this blog.

Here, we put our dry ice in a bowl of warm water. Water is constantly evaporating, and this warm water is no exception. As a result, the air above the water is very humid as it contains a lot of this evaporated water. One important thing about dry ice that hasn’t been mentioned yet: it’s cold. Like -109℉ cold. Brrr!

Adding it to the water causes air temperature to drop, forcing the water vapor in the air to condense. If it looks like fog, that’s because it is! We have simply made a low-flying cloud in a bowl! Clouds in real life form the same way. Warm air carries water vapour up into the high, cold parts of the atmosphere where they condense in the same way, minus the dry ice, of course.

The cloud forming is independent from the bubble expanding. This is a bit tricky. As the water vapor cools down and condenses it is not pushing out on the bubble. However, the dry ice is sublimating. the resulting carbon dioxide gas takes up more space. Unfortunately, CO2 is colorless. This makes it look like the cloud is blowing up the bubble, but really the cloud is just filling up the space that the sublimated dry ice is clearing out for it, until…

burst my bubble

The bubble bursts and the dense cloud falls to the ground, which looks really cool. It also raises a rather interesting question: If clouds are more dense than air, then what in the world are they doing way up there in the sky? The answer is a bit complex. The short version is that the tiny water droplets that make up clouds fall very slowly, but they tend to form in warm, rising, low pressure air that overcomes their slow fall, allowing them to float high in the sky.

clouds1
For more information, I recommend reading this article.

The Invisible Fire Extinguisher

You’ve heard of fighting fire with water, but did you know that gases also have the power to douse flames? A gas can smother a blaze by creating a barrier between burning fuel and nearby air.

Extinguisher1Removing any of the three requirements for fire stops the combustion reaction. Image credit: Ohio Northern University

Fire needs three things to burn: fuel, energy (heat), and oxygen. Take away any of these, and the combustion reaction can’t go on. Carbon dioxide gas is denser than air, so it sits nicely in a container and falls down like water when poured out. It’s also non-flammable, so it smothers burning fuel.

In this experiment, we scoop carbon dioxide gas into a pitcher, then pour it down a tube towards a row of candles. It’s invisible, but its interaction with the flames reveals its presence. As CO2 engulfs each candle, it isolates the wick from the surrounding oxygen. Without oxygen, the burning reaction stops!

Extinguisher2

Many household and industrial fire extinguishers take advantage of this science. Under high pressure, a lot of CO2 can be stored in a small space. Red canister extinguishers often contain reserves of carbon dioxide gas, ready to separate oxygen from burning fuel in an emergency.

Carbon dioxide is also stored under high pressure in the lab. When released into a container at room temperature, it condenses into a very cold solid– touch it for more than a split second, and you’ll experience the burn-like symptoms of contact frostbite.

You may know solid CO2 better as dry ice! Dry ice gets its name from a peculiar behavior: when it melts, it doesn’t make a puddle. This transition, straight from solid to gas without passing through a liquid state, is called sublimation.

sublimation-everest-large

Water can sublimate, too! Mt. Everest, with its high altitude, low pressure, dry air, and strong sunlight, is one place where ice turns directly into vapor. Image credit: Benjamin D. Oppenheimer (http://water.usgs.gov/edu/watercyclesublimation.html)

CO2 Fire Extinguisher

“Fire… begone!” These words aren’t magic, they’re science! We’ve harnessed the unique properties of a certain gas, carbon dioxide, to make our own version of a fire extinguisher. To understand how this works, we need to start with an understanding of fire. Fire requires two things in order to continue burning: fuel and oxygen. Without those fire will cease to exist. Our homemade fire extinguisher deprives fire of the second ingredient: oxygen.

We start with some dry ice. Dry ice is simply the solid form of carbon dioxide. When the dry ice heats up, it sublimates and turns into its gaseous form. Carbon Dioxide in its gas form is invisible and very dense. It’s density allows you to scoop it in a pitcher the same as you would a liquid, except that you can’t see it. When poured out it is heavy enough to push away all of the oxygen around the fire. No oxygen, no fire! Tada!

WELCOME TO OUR ASTROCAMP BLOG

We would like to thank you for visiting our blog. AstroCamp is a hands-on physical science program with an emphasis on astronomy and space exploration. Our classes and activities are designed to inspire students toward future success in their academic and personal pursuits. This blog is intended to provide you with up-to-date news and information about our camp programs, as well as current science and astronomical happenings. This blog has been created by our staff who have at least a Bachelors Degree in Physics or Astronomy, however it is not uncommon for them to have a Masters Degree or PhD. We encourage you to also follow us on Facebook, Instagram, Google+, Twitter, and Vine to see even more of our interesting science, space and astronomy information. Feel free to leave comments, questions, or share our blog with others. Please visit www.astrocampschool.org for additional information. Happy Reading!

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