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Humidity affect Density?

  1. Aug 10, 2005 #1
    Hi, as the topic stated, i would like to find out, does the humidity in the air affect the density??
    thanks
     
  2. jcsd
  3. Aug 10, 2005 #2

    minger

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    I wouldn't see how it couldn't. I would think you would need to do a partial pressures analysis to see the water content (prolly involving a psychometric chart). Then using a ratio of densities of water/air at that temperature to get the overall density.

    But this is definately just a guess.
     
  4. Aug 10, 2005 #3

    BobG

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    The molar mass of air is almost 29. The molar mass of water is 18. The more 'less dense' gas you have intermixed into the air, the less dense the air. So, yes, humid air is less dense than dry air.
     
  5. Aug 10, 2005 #4

    DaveC426913

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    Gold Member

    My gut tells me that humid air is more dense than dry air.
    (edit)
    My gut, apparently lies:

    http://www.usatoday.com/weather/wdensity.htm
    "Most people who haven't studied physics or chemistry find it hard to believe that humid air is lighter, or less dense, than dry air."

    BobG seems to be right on the money.
     
  6. Aug 10, 2005 #5

    Astronuc

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    Staff: Mentor

    That's exactly it - diatomic molecules N2 and O2 have approximate molecular masses of 28 and 32 (and air is 78+% N and 21+% O with traces of other gases), which in humid air are displaced by H2O, which has a molecular mass of 18.
     
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