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Ideal gas law constant R conversion

  1. May 6, 2004 #1
    Hi, not sure if this is the right forum to ask this in, but I was trying to convert the ideal gas law constant R (from PV = nRT) from:

    8.31 (Pa * cu. meters) / (mol * Kelvin) to the equivalent:

    10.73 (psia * cu. ft) / (lb. * mol * Rankine)

    Here's the conversion factors I've been using:
    1 Pa = 1.4505E-7 psia (absolute pressure)
    1 cu. meter = 35.315 cu. ft
    1 Rankine = 1.8 Kelvin

    What I don't understand is where does the extra pounds in the denominator of the 10.73 value come from? This is probably what's throwing off my calculations.

    -Thanks
     
  2. jcsd
  3. May 6, 2004 #2

    Doc Al

    User Avatar

    Staff: Mentor

    gm-Mole vs. lb-Mole

    In the first equation "mole" means "gram-Mole"; in the second the unit is "lb-Mole". You need to convert between gm-Moles and lb-Moles.
     
  4. May 6, 2004 #3
    Ahh, using 1 gram = 0.0022 lb I finally got it. Thanks alot, this has really been bugging me :smile:
     
  5. May 7, 2004 #4
    I always use this
    [tex]R = 0.082 \frac{atm \cdot l}{mol \cdot K} = 2 \frac{cal}{mol \cdot K} = 8.314 \frac{J}{mol \cdot K} [/tex]
     
  6. Jul 29, 2004 #5
    Take a look at:
    PDAcalc units This program runs on a palm, PocketPC,windows and will do all the conversions AUTOMATICALLY for you. Download the user manual which has an example of the PV = nRT formula that shows how it automatically convert between the different units.
     
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