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Homework Help: Getting strange answer , lease help

  1. Aug 10, 2006 #1

    xto

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    The question is
    a volume of 2.2m^3 of air at inital conditions of 1.2bar and 303K undergoes the following process to complete a cycle :

    i)isothermal compresssion from state 1 through a volumetric compression ration of 6 to state 2

    ii) isobaric expansion from state 2 back to the initial volume thus reaching state 3

    iii) isochoric cooling from state 3 back to the original pressure to reach state 1

    Q1) Find the mass of air present

    so i use the formula PV=nRT

    P=1.2bar
    V=2.2M^3
    n=?
    R=6
    T=303K

    so i need to find N so i got 2.64 = 1818N
    which N is 1.452x10^-3 :cry:
    which is total not the mass of the air , please help
     
  2. jcsd
  3. Aug 12, 2006 #2

    FredGarvin

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    Science Advisor

    R is the universal gas constant. It is not 6.
     
  4. Aug 12, 2006 #3

    berkeman

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    Staff: Mentor

    OMG, I just spit water all over my keyboard. :rofl:
     
  5. Aug 12, 2006 #4

    xto

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    ok , i kind of get it
    beacuse i'm given 2 R
    Rv is 6
    the other R is 0.287kJ/kg K

    so its

    (1.1832)x(2.2x10^3)
    ---------------------
    (0.287)x(303k)

    then i get 29.90g (to 2d.p) Air

    is that right for the mass of air present?


    By the way , thank you so much for the help
     
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