What is the Number Density of Gas Molecules at Sea Level?

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The discussion focuses on estimating the number density of gas molecules in the Earth's atmosphere at sea level, with an assumption of standard temperature and pressure (STP). The density of air at STP is noted as 1.3 kg/m^3, leading to a calculation using the ideal gas law, resulting in approximately 2.7 x 10^25 molecules/m^3. Participants suggest that if no temperature is specified, it is reasonable to assume standard temperature. An alternative method discussed involves calculating the weight of an air molecule to verify the number density using the known density of air. The calculations and assumptions presented align with standard practices in atmospheric science.
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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
 
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If they do not specify a temperature, assume standard temperature.

Looks good to me.
 
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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