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Homework Help: Dew point and absolute humidity

  1. Jan 10, 2015 #1
    1. The problem statement, all variables and given/known data
    Room temperature is 200C and relative humidity is 60%. what is the absolute moisture

    2. Relevant equations
    Vapor pressure at 200C=17.5[atm]
    Molecular weight of water=18[gr/mol]

    3. The attempt at a solution
    The vapor pressure at 200C:
    $$\frac{x}{17.5}=0.6\rightarrow x=10.5[atm]$$
    $$PV=nRT\rightarrow 10.5\cdot 1=n\cdot 0.08208\cdot 293\rightarrow n=0.437[mol]$$
    $$0.437\cdot 18=7.86[\frac{gr}{m^3}]$$
    It should be 10[gr/m3]
  2. jcsd
  3. Jan 10, 2015 #2
    That should be mm Hg.
    Again, that should be mm Hg
    The gas constant value you used here for liters. You also need to use a pressure of 10.5/760 atm.

  4. Jan 10, 2015 #3
    $$\frac{x}{0.023}=0.6\rightarrow x=0.0138[atm]$$
    $$PV=nRT\rightarrow 0.0138\cdot 1[liter]=n\cdot 0.08208\cdot 293\rightarrow n=0.000574[\frac{mol}{liter}]=0.574[\frac{mol}{m^3}]$$
    $$0.574\cdot 18=10.3[\frac{gr}{m^3}]$$
  5. Jan 11, 2015 #4

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