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Homework Help: More gas law problems

  1. Oct 13, 2008 #1
    what volume is occupied by 2.0 g of He at 25 degrees C and a pressure of 775 mm?
  2. jcsd
  3. Oct 13, 2008 #2
    [tex] Pv = nRT [/tex]

    P = pressure
    v = volume
    n = number of moles
    R = universal gas constant
    T = temperature.

    Calculate how many moles are in 2.0 grams of helium, divide both sides of the equation by P.


    EDIT: Remember to have your units correct, IE Kelvin, kilograms etc
  4. Oct 13, 2008 #3
    what is the constant? or is there one? if so, how do i determine what it is?
  5. Oct 13, 2008 #4
    R is the universal gas constant. It is always the same. In si units, it is: 8.314472 Joules per mol kelvin.
  6. Oct 13, 2008 #5
    ok, im not sure about this, but is the answer 1.59?
  7. Oct 13, 2008 #6
    What did you use as your numbers?
  8. Oct 13, 2008 #7
    775=0.5(constant)(298), then divided by 775
  9. Oct 13, 2008 #8
    That equation is: [tex] p = nRT [/tex]
    You need volume on the left hand side to solve for it.
    Also, you wrote in the question description that pressure = 775mm, I am going to assume that this is mmHg.
    You are going to need to convert this to pascals.
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