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Thread: Dry Ice/CO2

  1. #1 Dry Ice/CO2 
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    I know dry ice is frozen CO2 and it sublimates directly from solid to gas. My question concerns the other direction. Everything I have found on the creation of dry ice starts with liquid CO2 and high pressure. The pressurized liquid is then allowed to expand, causing dry ice to form (if I understood what I read).

    So my question is: Assuming you are at sea level, what happens when you take CO2 gas and cool it past it's freezing point? It seems to me that the result should still be solid CO2. But then why go through the trouble of liquid CO2 to make dry ice?


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  3. #2  
    Forum Sophomore Matt Lacey's Avatar
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    Carbon dioxide doesn't have a liquid phase at atmospheric pressure no matter which direction the transition is in.

    You use pressurised CO2 to make dry ice because what would you cool CO2 gas with? It's really easy to make dry ice from a pressurised cannister of CO2, you just open the valve and let the gas quickly expand into some container so you can collect it, easy peasy. Pressurisation is something mechanical that's easily controllable.


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  4. #3  
    Forum Senior anand_kapadia's Avatar
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    I have also read about dry ice and was unable to understand how can a gas be pressurised and then on releasing the pressure why does it not change to the same gaseous form.
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  5. #4  
    Forum Sophomore Matt Lacey's Avatar
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    Look up Charles' Law, all about the relationship between volume and temperature.
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  6. #5  
    Forum Sophomore basim's Avatar
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    It is quiet like a molecular problem
    molecules of CO2 at gas phase are far apart.
    when pressurized it becomes closer enough. than by cooling it becomes solid.
    but if we cool the gas, molecules are too far apart to freeze it
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  7. #6  
    Forum Sophomore Matt Lacey's Avatar
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    No, because the volume decreases as you cool it.
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  8. #7  
    Forum Professor leohopkins's Avatar
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    Is it possible to buy soemthing (for my home) - actually for my PC. Which creates dry ice ?
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  9. #8  
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    http://www.day-impex.co.uk/dryicemaker.asp

    CHeck that out, you'll need a cylinder of liquid CO2 though....
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  10. #9  
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    There is another product I saw on frostic.com. It is built for home and professional use. They produce about 1 pound of dry ice per minute. And yes, you do need your own source of liquid CO2.
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