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Homework Help: Ideal gas theory

  1. Jul 13, 2010 #1
    1. The problem statement, all variables and given/known data

    a) An ideal gas has a pressure of 1atm, volume of 0.5m^3m temperature of 300k. Find the number of moles.

    b) Three moles of an ideal gas is at a pressure of 1x10^2 Nm^-2 and a temperature of 263K. Calculate the volume.

    2. Relevant equations

    1) PV = NRT
    2) PV=NKbT

    R = gas constant; Kb = Boltzman's constant

    3. The attempt at a solution

    I have found the answers to be a) 1.22x10^23moles and b) 65.6m^3.

    What I don't understand, is when to use which equation. Why can I not use equation 1) for question a) vice versa.

  2. jcsd
  3. Jul 13, 2010 #2
    Answer (a) is wrong. In PV = nRT, the "n" stands for moles. In PV = NkT, the "N" stands for number of molecules. There are 6.022 x 1023 molecules in a mole.
  4. Jul 13, 2010 #3
    Sorry that was meant to be 1.22x10^25 molecules.

    Thank you for explaining.
  5. Jul 13, 2010 #4
    Okay. I didn't check your math, but aren't you asked for the number of moles, rather than the number of molecules?
  6. Jul 13, 2010 #5
    Woops I was meant to write molecules instead of moles for question a) in my first post.

    Must remember to re-read my posts before submitting them. Sorry about that!
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