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Liquid with the densest vapor

  1. Oct 5, 2014 #1
    1. The problem statement, all variables and given/known data
    Which of the following liquids would form the densest vapor upon heating?
    A. CH3CH2CH2OH
    B .CH3(CH2)3CH2Cl
    C. CH3(CH2)4CH2Br
    D. (CH3)3CCH2OH

    2. Relevant equations
    None really

    3. The attempt at a solution
    Now I know the answer already, its C. My question is why? I got B, my reasoning was that it is the lightest and has the least inter-molecular forces, which would result in a higher vapor pressure at a given temperature. Now the solution states it is C because at standard conditions, the molar volume is roughly the same. Does this mean, at the same temperature and pressure, the vapor pressure above each solution will be roughly the same?
     
  2. jcsd
  3. Oct 5, 2014 #2

    Borek

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    Staff: Mentor

    Which gas is more dense: hydrogen, or sulfur hexafluoride?
     
  4. Oct 5, 2014 #3
    That would be sulfur hexafluoride. But my confusion is that in the question, the molecules are liquids and are producing vapor while still in the liquid phase. So is the question that I posted asking about which vapor is densest when both are produced to equal volume? Don't they have different imf and M.W. so that each liquid produces different amounts of vapor pressure at a given temperature?
     
  5. Oct 5, 2014 #4

    Borek

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    Staff: Mentor

    Different pressures of the saturated vapor for sure, but I don't think you have enough information to judge that (especially when there are opposite effects at work). Approach based just on the molar mass is easy to defend - you compare things assuming everything else is identical.
     
  6. Oct 5, 2014 #5
    Ah I see, that'll be important to consider in future questions. Thanks!
     
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