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Homework Help: Using Ideal Gas Law to find P, V, or T

  1. Dec 16, 2009 #1
    Ok, so I'm doing this homework online and I THINK I'm doing it correctly, but I'm getting incorrect answers.

    1. The problem statement, all variables and given/known data

    0.290 mol of argon gas is admitted to an evacuated 40.0 cm^3 container at 60.0 degrees C. The gas then undergoes an isochoric heating to a temperature of 300 degrees C.

    What is the final pressure of the gas?

    2. Relevant equations

    p=(nRT)/V and p(f)/T(f)= p(i)/T(i)

    3. The attempt at a solution

    Okay, so I need to find p(i).
    n=.290 mol
    V=40 cm^3 = 40cm^3(1m/100 cm)^3 = 4x10^-5 m^3
    T= 60.0 degrees C = 60 C + 273 = 333 K
    R= the ideal gas constant which is 8.31 J/mol K

    Therefore,
    p(i)= (.290 mol * 8.31 J/mol K * 333 K)/ (4x10^-5 m^3)
    p(i) = 2.01x10^7 atm

    Now that I know p(i), i can then solve for the temperature increase to find p(f)

    p(f) = p(i)T(f)/T(i)
    p(f) = (2.01x10^7 atm * 573 K)/ 333 K = 34586486 atm = 3.46x10^7 atm

    They want the answer in kPa, and converting atm to kPa online yielded 3.50x10^10.

    I'm completely clueless as to what I'm doing wrong. There are two other problems asking for either p or V which seem to have the same basis. If I can figure out what I'm doing wrong here, I should be able to understand why I'm doing the rest wrong. Thank you.
     
  2. jcsd
  3. Dec 16, 2009 #2
    Ah, disregard my question. I was mistaken when I thought that pressure in p=nRT comes out in atm. It actually is in Pa and you have to change 3.46x10^7 to 3.46x10^4.
     
  4. Dec 16, 2009 #3

    Borek

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    Staff: Mentor

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