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Homework Help: Temperature/Ideal Gas Problem

  1. Oct 6, 2008 #1
    1. The problem statement, all variables and given/known data
    Well, I did get an answer to this, but I don't think I did it right. It kinda seems wrong to me, so I wanted a second opinion :)

    At 25 m below the surface of the sea (Density = 1025 kg/m^3), where the temperature is 5 degrees Celsius, a diver exhales an air bubble having a volume of 1 cm^3. If the surface temp of the sea is 20 degrees Celsius, what is the volume of the bubble just before it breaks the surface?


    2. Relevant equations
    Ideal gas: PV = nRT
    P = Po + (DENSITY)gh ??Not sure if I should use this??


    3. The attempt at a solution

    P = Po + Density(g)(h) = 1.013 x 10^5 Pa + (1025)(9.81)(25)
    P = 3.5 x 10^5 Pa (This seems fairly logical to me... kinda? But I'm not very logical :P)

    Under the sea
    (3.5 x 10^5)(0.01 m^3) = n(3.814)(278 degrees K)
    n = 3.3
    At surface
    (1.013 x 10^5)(V) = (3.3)(3.814)(293)
    V = 0.036 m^3, or 3.6 cm^3... that's fairly reasonable, isn't it?? But I'm not sure if using the P = Po + density(g)(h) was all right when the height is below the sea like that ??
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Oct 6, 2008 #2

    mgb_phys

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    Science Advisor
    Homework Helper

    You can use pv=nRT remember that 'nR' isconstant.
    Then you just need to find the pressure at 25m underwater, p = density * g * h
     
  4. Oct 7, 2008 #3
    Forgive me if I sound dense (I may very well be!) but isn't that kind of what I did? If it's been smart enough to note they were constant, I could have done it with less work
     
  5. Oct 7, 2008 #4

    Borek

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    Staff: Mentor

    Looks OK to me.
     
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