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Homework Help: Cooling bath temperature question

  1. Nov 10, 2011 #1
    1. The problem statement, all variables and given/known data

    A cooling bath is prepared in a laboratory by mixing chunks of solid CO2 with ethanol. CO2(s) sublimes at -78.5°C to CO2(g). Ethanol freezes at -114.5°C and boils at +78.4°C. State the temperature of this cooling bath and describe what will be seen when it is prepared under ordinary laboratory conditions.

    The answer is -78.5°C.

    2. Relevant equations

    Not sure if there are any equations. Might just be a graph with a critical point or something like that.

    3. The attempt at a solution

    First of all, the definition of a cooling bath is a bath that maintains a low temperature close to 0°C right? I suppose that the mixture of CO2 and ethanol is with solid CO2 (given) and liquid ethanol, so does the ethanol break up the CO2 or something? Anyway at -78.5°C ethanol is still liquid and CO2 is just in between solid and gaseous state. I don't understand how the answer is -78.5°C and I also would like to understand what happens in the cooling bath like the question states.

    Thank you! :)
  2. jcsd
  3. Nov 10, 2011 #2


    User Avatar

    Staff: Mentor

    It is mostly about the latent heat - question assumes there is enough solid carbon dioxide used.

    Mixture is prepared using ethanol at - most likely - room temperature, so it will be cooled down by subliming CO2. How far down can the temperature go?
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