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Homework Help: Gas Laws

  1. Jan 7, 2008 #1
    Hey guys, I was wondering if anyone could help me out with this problem?

    If you place 10.0L of methanol (CH4O) in a sealed room that is 3 m long, 1.75 m wide, and 2.5 m high, will all the methanol evaporate? If some liquid remains, how much will there be? The vapor pressure of methanol is 127 torr at 25 degrees C, and the density of the liquid at this temperature is 0.791 g/mL.

    I'm not quite sure how to get this problem started.

    I know that 127 torr = 127 mmHg/760 mmHg = 0.167 atm
    and PV = (10.0 L)(0.167 atm) = 1.67 L*atm
    and PV = nRT
    =(0.167 atm)(10.0 L)/(0.0821 L*atm/K*mol)(298 K)
    =0.0683 mol

    but I'm not sure if I'm on the right track or how to fit these pieces together. could somebody please, please, please help me?
  2. jcsd
  3. Jan 7, 2008 #2


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    You are in the right chapter but not the right track. The gas law doesn't work for the 10L of liquid methanol... only for gases.

    Calculate how many grams of methanol you have in 10L and from that you can calculate the number of moles. Use the ideal gas law only to find out how many theoretical moles of gas are possible in the room. You will need to make an assumption as to whether the room contains air or is evacuated before the methanol is introduced.
  4. Jan 7, 2008 #3
    Ah you're a genius! I can't believe the difference in phases didn't even cross my mind.
  5. Jan 8, 2008 #4
    Thanks a lot Chemisttree! I have found the errors of my ways (and there were a few). Thanks again for pointing me in the right direction.
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