Why does dry ice produce visible smoke if CO2 is normally invisible?

[GrizzlyBat]

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?

 

[Backscattered]

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.

 

[Mapes]

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.

 

[Backscattered]

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.

 

[Bob S]

It could be that the temperature drop of the air is causing the relative humidity of the air to reach 100%.

 

[Danger]

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.

 

[Vanadium 50]

The smoke is condensing water vapor - small snowflakes or droplets of water. Capture it on an object and it gets wet.

 

[Dadface]

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.