The Mystery of Dry Ice Smoke: Is it CO2?

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Discussion Overview

The discussion revolves around the visibility of the smoke produced by dry ice, questioning whether it is actually carbon dioxide (CO2) or a result of other factors, such as moisture in the air. Participants explore the phenomenon from various angles, including physical properties, atmospheric conditions, and experimental observations.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant questions whether the visible smoke from dry ice is actually CO2, suggesting that it does not make sense to see CO2 evaporating, as it is normally invisible.
  • Another participant explains that the smoke is a result of sublimation, where solid CO2 converts directly to gas, creating a dense area of CO2 gas that appears to dissipate quickly.
  • A different viewpoint challenges the visibility of gaseous CO2 at atmospheric pressure, proposing that the smoke is likely condensed water droplets from the surrounding air due to the low temperature of the dry ice.
  • One participant mentions observing a similar phenomenon in a dry nitrogen/CO2 atmosphere, raising the possibility of residual water in the system affecting visibility.
  • Another participant suggests that the temperature drop caused by dry ice may lead to the air reaching 100% relative humidity, contributing to the visible effect.
  • Several participants agree that the visible smoke is primarily condensed atmospheric water, emphasizing that CO2 itself is invisible.
  • One participant draws a parallel between the condensation seen with dry ice and the condensation on a cold glass, further illustrating the point about water vapor.

Areas of Agreement / Disagreement

Participants generally agree that the visible smoke is related to condensed water vapor rather than CO2 itself. However, there are differing opinions on the exact mechanisms and conditions that lead to this visibility, indicating that multiple competing views remain.

Contextual Notes

Some assumptions about the conditions under which the observations are made, such as atmospheric pressure and humidity levels, are not fully explored. The discussion also does not resolve the specific nature of the gas behavior in different environments.

GrizzlyBat
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Does anyone know why you can see the smoke coming from dry ice? Is it actually CO2? It does not make sense to me, why could I see CO2 evaporating, but I cannot see it normally? Is it the moisture in the air that I can see reacting with the cold CO2?
 
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What you are seeing is the sublimation point where the solid CO2 is converting directly to gas. The smoke as you describe really is nothing more then a dense area of CO2 gas (due to is still low temperature) which quickly expands and dissipates which makes it appear to disappear.
 
Backscattered said:
The smoke as you describe really is nothing more then a dense area of CO2 gas (due to is still low temperature) which quickly expands and dissipates which makes it appear to disappear.

I've never heard of gaseous CO2 being visible anywhere atmospheric pressure, so I severely doubt this. It's far more likely that when you're seeing is water droplets condensed out of the surrounding air due to the low temperature.
 
Good point, and certainly reasonable, though I have seen the same phenomenon in a dry nitrogen / Co2 atmosphere set at normal atmosphere pressure... maybe there was still some h20 in the system? Anyway good luck with your discoveries.
 
It could be that the temperature drop of the air is causing the relative humidity of the air to reach 100%.
 
I agree that what you see is condensed atmospheric water. CO2 is invisible. When you use dry ice to make 'smoke', such as for a party, you put it into a tub of water.
 
The smoke is condensing water vapor - small snowflakes or droplets of water. Capture it on an object and it gets wet.
 
Vanadium 50 said:
The smoke is condensing water vapor - small snowflakes or droplets of water. Capture it on an object and it gets wet.

A bit like the condensation on the outside of my glass of cold beer.Cheers.
 

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