1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
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: Atomic Density.

  1. May 24, 2009 #1
    1. The problem statement, all variables and given/known data

    Hi, Im not sure about the following question:

    (Q) Argon (atomic weight 40) exists as a monatomic gas at room temperature and pressure. The density of liquid argon is 1784kg/m^3.

    (a) Calculate the atomic density (atoms/m^3) in liquid argon *Done*

    (b) Hence assumming the packing fraction in liquid argon is 0.7, determine the radius of an argon atom. *Done*

    (c) calculate the atomic density in gaseous argon at a pressure of 1atm and a temperature of 300K *Done*

    (d) hence calculate the mean free path of an argon atom at a pressure of 1 atm and a temperature of 300K?

    2. Relevant equations

    It is part (d) which I'm having trouble with

    The mean free path formula is 1/[(4pi)nσ²]

    3. The attempt at a solution

    For part (d) which 'n' should I use the one for gas argon or for liquid argon, the question given doesnt seem to state which mean free path to calculate?
  2. jcsd
  3. May 24, 2009 #2


    User Avatar
    Homework Helper

    The 'hence' suggests they want you to calculate it for gaseous argon.
  4. May 25, 2009 #3
    Oh Hi! right! I actually forgot the next question which was:

    (e) Calculate the root mean square of an argon atom at a temperature of 300K.

    Again do you calculate it for gaseous or liquid argon? and why would they put both types of argon in the same question, its confusing..and they dont really ask any questions about comparing both types at the end.

    I also found another question very similar to the above but how do I tackle this one?

    (Q2.) The viscosity of argon gas (atomic weight 40) at a temperature of 273K and a pressure of 1atm is equal to 2.1 x 10^5 Pa s. The density of liquid argon is 1784kg/m^3 . Use these two pieces of data to determine the mean speed of an argon atom at 273k, its effective radius and Avogadro's number.
  5. May 25, 2009 #4


    User Avatar
    Homework Helper

    What is the boiling point of argon?
  6. May 25, 2009 #5
    87.3K approx, how does this help me?
  7. May 25, 2009 #6


    User Avatar
    Homework Helper

    Seeing as the temperature of argon in question e) is 300K it would stand to reason that they are interested in gaseous argon.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook