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Number Density of Air

  • Thread starter bcjochim07
  • Start date
  • #1
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Homework Statement


Estimate the number density of gas molecules in the earth's atmosphere at sea level.

Homework Equations





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:
PV=NkT

P/kT =N/V
(101300Pa)/(1.38E-23)(273 K)=2.7 * 10^25 molecules/m^3
 

Answers and Replies

  • #2
G01
Homework Helper
Gold Member
2,665
16
If they do not specify a temperature, assume standard temperature.

Looks good to me.
 
  • #3
mgb_phys
Science Advisor
Homework Helper
7,774
12
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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