Three phases of CO2 can be observed doing this simple demo.
WATCH VIDEO
Teachable Topics
- Phase Transitions
- Temperature and Pressure
- Atomic Structure
Theory
Whether a substance is existing as a solid, liquid, gas, etc depends mostly upon external factors such as temperature and pressure. For carbon dioxide (CO2), a quick look at its phase diagram shows that at room temperature (about 25C or 300K), it can exist as any of the three phases depending upon its pressure.
Solid CO2 is what we call dry ice. In this experiment, we place some shavings of dry ice into a strong glass vial with a tight fitting lid. As the dry ice sublimates into its gaseous form, the pressure in the vial increases dramatically. The pressure (and temperature) increase is such that eventually, the CO2 condenses into its liquid form!
Upon opening the vial of liquid CO2, the outreach of air is sufficient to immediately chill the vial enough to recondense the liquid/gas mixture into a solid again!
Apparatus
- Dry ice
- Cryogen gloves
- Faceshield
- Sturdy glass or transparent glass vial with tight enclosure.
Procedure
- Scoop some dry ice into the vial. Close the lid tightly.
- As the container warms up and the internal pressure increases, the dry ice will turn into gas and then into liquid.
- Open the container quickly and, if it hasn't gotten too warm, the carbon dioxide will turn back into ice.
Safety
- Be careful not to expose your skin to dry ice.
- You must use a solidly built glass vial for this demo or else you risk the possibility that the vial will shatter under the increased pressure. We highly recommend you wear a faceshield when performing this demo in case that happens.
- Be very careful the container will not explode under pressure.
