(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

Calculate the mass of a mole of dry air, which is mixture of N_{2}(78 percent by volume, O_{2}(21 percent) and argon (1 percent).

Use the ideal gas law to write the density of air in terms of pressure, temperature , and the average mass of the air molecules. Show , then, that the pressure obeys the differential equation

dP/dz=-mgP/kT

2. Relevant equations

PV=nkT

3. The attempt at a solution

m(total)=.78(28 grams)+.21(16 grams)+.01(40 grams)= 29 grams

rho=m/V , from Ideal gas law, V=nKT/P ==> rho=m*P/nkT

I am having difficulties with show that dP/dz=-mgP/kT. I know other thread on the ideal gas law problem concerning the same problem I said that dP/dz=-rho*g. and I know that rho=mP/nkT, therefore I guess dP/dz=rho*g=mgP/nkT. The only problem is how would I get rid of n? Should I assume that they are talking about one mole of air and therefore n=1?

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# Homework Help: Ideal gas law problem: part 2

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