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Homework Help: Number Density of Air

  1. Apr 29, 2008 #1
    1. The problem statement, all variables and given/known data
    Estimate the number density of gas molecules in the earth's atmosphere at sea level.

    2. Relevant equations

    3. The attempt at a solution

    The question doesn't give me any further information and I am wondering about temperature---should I just say it's at STP? I found in my book that the density of air at STP is 1.3 kg/m^3.

    Here's what I did:

    P/kT =N/V
    (101300Pa)/(1.38E-23)(273 K)=2.7 * 10^25 molecules/m^3
  2. jcsd
  3. Apr 29, 2008 #2


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    Homework Helper
    Gold Member

    If they do not specify a temperature, assume standard temperature.

    Looks good to me.
  4. Apr 29, 2008 #3


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    Science Advisor
    Homework Helper

    As a check / alternative - work out how much an 'air' molecule weighs and use the density to work how many molecules.
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