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

[bcjochim07]

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

 

[G01]

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

Looks good to me.

 

[mgb_phys]

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