Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Ideal Gases

  1. Dec 3, 2007 #1
    [SOLVED] Ideal Gases

    1. The problem statement, all variables and given/known data
    A gas has a temperature of 310K and a pressure of 101kPa (a.) find the volume occupied by 1.25 mol of this gas, assuming its ideal. (b.) assuming the gas molecules can be approximated as a small sphere of diameter 2.5x10^-10, determine the fraction of the volume found in part (a) that is occupied by the molecules.

    2. Relevant equations

    3. The attempt at a solution
    (a.) V=nRT/P
    V= (1.25mol)(8.31J/mol*K)(310K)/0.101Pa
    V= 31882.43 m^3

    (b.)d= 2.5x10^-10
    V(sphere)= 8.18x10^-30

    n= (.101Pa)(31882.43m^3)/(8.31J/mol K)(310K)
    n= 1.25 mol *6.022x10^23= 7.5275x10^23 molecules

    do i just multiple these together and then find the fraction from the first volume?
  2. jcsd
  3. Dec 3, 2007 #2

    Chi Meson

    User Avatar
    Science Advisor
    Homework Helper

    Yes, that works fine.

    but notice, Vsphere/V can be determined without ever knowing n.

    Since this fraction should not depend on how large your sample is, the number should "cancel out." solve for this fraction using variables (without plugging in numbers) and you will see n go away.
  4. Dec 3, 2007 #3


    User Avatar
    Homework Helper

    For the first part...1kPa=1x10[itex]^3[/tex]Pa
    and for the fraction occupied, vol.occupied by gas/vol.of sphere
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook