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Homework Help: Question on relative humidity

  1. Jul 29, 2009 #1
    1. The problem statement, all variables and given/known data

    Temperature of a closed room is 15 degree celsius (T288).Relative humidity(RH)at 15degree celsius =60%
    Find the RH when the temperature is 20 degrees.
    S.V.P at 15 degrees celsius=12.67mmHg
    SVP at 20 degree celsius = 17.36mmHg
    (ans:45%)
    2. Relevant equations



    3. The attempt at a solution
    RH= [Partial pressure at 15 degree celsius(P15)/SVP at 15]*100%

    P15V = m1rT288 ----------(1)
    p20V=m2rT293 -----------(2)

    I get the answer when i take m1 as equal to m2,but I don't understand why they should be equal.
    Doesn't m,the mass of water vapour present in the room increase with temperature?

    Thanx
     
  2. jcsd
  3. Jul 29, 2009 #2

    tiny-tim

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    Science Advisor
    Homework Helper

    Hi leena19! :wink:
    Always study the question …

    it's a closed room! :rolleyes:

    Where would the extra mass come from? :smile:
     
  4. Jul 29, 2009 #3
    Ah!OK.
    Thank you very much!
     
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