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Explanation of the characteristics of dry ice - Succeed in Physical Science. Also refer to physical science, freezing, carbon dioxide, CO2, sublimation, deposition, liquid, solid, gas, ice, Fahrenheit, Celsius, Ron Kurtus, School for Champions. Copyright © Restrictions
Dry Ice
By Ron Kurtus (revised 1 December 2005)
Frozen carbon dioxide (CO2) is called dry ice. It is extremely cold and has the unusual feature that when dry ice melts under normal conditions, it goes directly from the solid form to the CO2 gas. Dry ice will melt into a liquid under high pressure. Dry ice is often used for handy refrigeration and for special-effects demonstrations.
Questions you may have include:
- How cold is dry ice?
- Why does it go from a solid to a gas?
- How is it used?
This lesson will explain those questions. There is a mini-quiz near the end of the lesson.
Useful tools: Metric-English Conversion | Scientific Calculator.
Temperature
Dry ice is frozen CO2 gas. The freezing temperature at normal sea level air pressure is -78.5 degrees C (-109.3 degrees F).
Although a block of dry ice looks relatively harmless, a person should use caution in handling the material because of its extremely low temperature. It could easily cause frost burns on the skin.
Using safety gloves when handling dry ice blocks
Another hazard is the fact that when dry ice melts, the result is carbon dioxide gas. Since CO2 gas is heavier than air, it settles to the bottom. In some rare cases, it could cause suffocation.
Solid to gas
At standard pressures and common temperatures, a material goes from a solid to liquid to gas. Water is a good example, where it goes from steam to water to ice, as the temperature drops.
But at higher pressures, it is possible to skip the liquid phase altogether. The process of going directly from a solid to a gas is called sublimation. Going the other direction from a gas to a solid is called deposition.
The illustration below shows the states of CO2 at various pressure and temperature combinations. At 1 atmosphere of pressure--which is the everyday air pressure we experience--carbon dioxide gas will freeze and turn to dry ice at about -78° Celsius. If you put the gas in a compression chamber and increased the air pressure about 5 times the normal pressure or 5 atmospheres, then CO2 will go from gas to liquid to solid. In other words, at say 7 atmospheres, dry ice will melt and become liquid CO2.
Change of state of CO2 at different pressures and temperatures
Uses
Dry ice is often used to keep food and other items cold in a container, such as an ice box.
Another common use is seen in movies and novelty displays. When pieces of dry ice are dropped in a container of water, they rapidly melt, causing a bubbling effect in the water, as if it was boiling. The CO2 gas bubbles out and looks like smoke. Movies about mad scientists and Halloween displays often use this effect.
When CO2 is at higher pressures, it exists in the liquid state. Liquid carbon dioxide is used in high-pressure fire extinguishers.
Summary
Dry ice is frozen carbon dioxide. It is extremely cold and will go directly from the solid form to gaseous state under normal conditions. Dry ice will melt into a liquid under high pressure. It is often used for refrigeration and special-effects demonstrations.
Learn how special effects work
Resources and references
The following resources provide information on this subject:
Websites
Books
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Mini-quiz to check your understanding
If you got all three correct, you are on your way to becoming a Champion in Physics. If you had problems, you had better look over the material again.
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Dry Ice