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Question on water vapour and pressures

  1. May 26, 2009 #1
    1. The problem statement, all variables and given/known data

    20 litres of moist air at 25 degrees celsius with a relative humidity of 75% are compressed isothermally to a volume of 4 litres. Calculate the mass of water condensed? (One method, find the original water vapour pressure, it will be increased by what factor?)

    2. Relevant equations

    pV= mRT

    water vapour pressure = density x R x T

    3. The attempt at a solution

    Where should I start with this problem. Finding the mass is really hard here, the mass of water condensed is only part a of the question. if i had that, i could figure it all out. any hints in the right direction?
     
  2. jcsd
  3. May 26, 2009 #2

    Borek

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    Staff: Mentor

    What is pressure of saturated water vapour at 25 deg C?
     
  4. May 26, 2009 #3
    sorry borek u lost me. am i supposed to read the pressure of saturated water vapour at 25 degrees off a chart? Because right now, I cannot see an equation that help me find the mass with the current information provided.
     
  5. May 26, 2009 #4
    yea think i got it. I used the chart to search for saturated vapour pressures at 25 deg C, then used PV= mRT to calculate the mass of water. Then use relative humidity to find mass of water condensed.

    cheers anyway
     
  6. May 26, 2009 #5

    Borek

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    Staff: Mentor

    Yes.
     
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