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Homemade dry ice

  1. Nov 20, 2014 #1
    what is Deposition, also known as desublimation, point of co2 is it room temperature? i dont think so then how can we obtain this at room temperature as in this video and what pressure is required to solidify co2,is it 1 atm ?i don't think so then how we obtain this in a room as in above mentioned video.
    i have searched a lot and came to know that
    The process is not at room temperature .The extinguisher contains liquid CO2 at room temperature and several atmospheres pressure. When it is discharged the pressure drops to one atmosphere and, as it falls, the liquid boils. The heat of vaporization greatly cools the expanding CO2 and it solidifies.is this much right?and i am still confused about pressure.When high pressure co2 liquid is discharged the pressure drops to one atmosphere ,but what is the pressure when co2 solidifies ?1 atm?how?
     
  2. jcsd
  3. Nov 20, 2014 #2

    Borek

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    Staff: Mentor

    Process takes place at approximately 1 atm.
     
  4. Nov 20, 2014 #3
    thanks .you mean when dry ice is formed from fire extinguisher pressure is1 atm.and what about temperature?he process is not at room temperature .The extinguisher contains liquid CO2 at room temperature and several atmospheres pressure. When it is discharged the pressure drops to one atmosphere and, as it falls, the liquid boils. The heat of vaporization greatly cools the expanding CO2 and it solidifies.is this much right?
     
  5. Nov 20, 2014 #4

    Borek

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    Staff: Mentor

    You are mostly right. How far the temperature drops is not easy to calculate, but we know it has to be at least sublimation temperature for the dry ice.

    Please pay attention to punctuation, as at the moment your posts are annoyingly difficult to read. There should be a space after every punctuation mark, and phrases should start with a capital letter.
     
  6. Nov 20, 2014 #5
    Thanks. From now onwards i will take care of my punctuations.
     
  7. Nov 28, 2014 #6
    We need the phase diagram to understand what's going on...

    media%2F654%2F654abc63-5ebf-4f33-9507-c38acd719f38%2FphpAsNMSr.png So...the fire extinguisher is at room temperature, lets say 31C...If we follow the temp line up we see the pressure in the cylinder is 72.9 Atm.... the cylinder contains liquid CO2 and gaseous CO2.

    When the fire extinguisher is operated the liquid exits the cylinder and finds itself at 1 Atm. it boils , giving off CO2 gas and rapidly cools .
    At 1Atm only solid and gaseous CO2 exist. Same at 5 Atm., but if we did this on a planet with 6Atm. pressure we get liquid and gaseous CO2 and perhaps some solid CO2.

    At 1Atm dry ice cannot be hotter than -78.5C and at 5.1 Atm. dry ice cannot be hotter than -56.7C

    All your questions can be answered by carefully studying the phase diagram.
     
    Last edited: Nov 28, 2014
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