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Homework Help: Molecules In Air

  1. Oct 3, 2004 #1
    Air at STP has pressure p = 1 atm = 1.013 ×105 Pa, and temperature T = 273 K. Use the ideal gas law to determine the number of molecules in a cubic meter of air.

    I have tried many different numbers and cant seem to get the correct answer. I guess I should use the formula

    PV = NkT

    P = 1 atm or 101.3 kPa? i tried both
    V = 1 m^3 or 1000 L? also tried both
    T = 273 K
    k = 8.617385 x 10-5 eV/K?

    so (101.3 kPa)(1000 L) = N (8.617385 x 10-5 eV/K)(273 K)

    do you see what i am doing wrong?

  2. jcsd
  3. Oct 3, 2004 #2
    For these units, use k=universal gas constant=R=8.314. I forget the units, but they cancel properly for kPa, L, moles, and Kelvin in the formula. Also remember that when you find N, that is the amount in moles (you must convert to molecules).
  4. Oct 3, 2004 #3
    no, nRT would give me moles, NkT gives me molecules
  5. Oct 3, 2004 #4
    nvm you were right, i got wrong info off a webpage

    thanks a ton
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