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Gas pressure

  1. Sep 29, 2009 #1
    1. The problem statement, all variables and given/known data
    An Aerosol has a of pressure 250kpa at 17 C.The aerosol is left in the sun and its temp.rises to 27 C.Calculate new pressure in the can if its a 35% increase in the amount of vapour present.


    2. Relevant equations
    P/T= constant


    3. The attempt at a solution
    well tbh i am just confused.. do i get T= into kelvin, ok i tried that too...
    my first attemp was:
    1)(273.15+27)-(17+273.15)=10kelvin
    so what i did:10x250x10^3/100= 25kPa
    so pressure at 27 is: 250+25=275Kpa
    2)
    2nd attempt:
    PV=nRT
    P/T=nr/v
    =>P/T= constant
    250x10^3/10kelvin=25kpa... which if i add to 250 gives me same answer.. lol i have confused my self badly -(. first i forgot to convert C into Kelvin .
    Thanks for the replies in adv.
     
  2. jcsd
  3. Sep 29, 2009 #2
    Try and work in an ordered way. Always try and structure your work in advance. Write out what you know, and what you're looking for.

    And I think you shouldn't work with [tex]P/T=constant[/tex]
    That's just a misleading way of saying that the volume is constant, and I think it can only lead to confusion.

    Initial state:

    [tex]P_1 V_1 = nRT_1[/tex]

    [tex]P_1= 250kPa[/tex]

    [tex]V_1=V_2[/tex] (As long as the can doesn't deform, its total volume remains the same)

    [tex]T_1=(17+273.15) ^o K[/tex]

    Final state:

    [tex]P_2 V_2 = nRT_2[/tex]

    We are looking for [tex]P_2[/tex]

    [tex]V_2=V_1[/tex]

    [tex]T_2=(27+273.15) ^o K[/tex]

    Now all that you need to do is isolate [tex]P_2[/tex] and express it in terms of known quantities.
     
    Last edited: Sep 29, 2009
  4. Sep 29, 2009 #3
    ermm sorry i dont get it , do you mean that i should isolate p2 =nRT2/v2
     
  5. Sep 29, 2009 #4
    Yes...
    Now find a way to express [tex]V_2[/tex] in terms of known quantities.
     
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