what does air weigh...?

What does 100 cubic feet of air weigh at sea level, at both 70 and 80 degess f. ? sorry, I'm bad with numbers. Thanks for your help!

yupchagee2006-11-23T10:08:17Z

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PV=nRT
n=PV/RT

R=10.7316 ft³ · psi · °R-1 · lbmol-1
P=14.7 psi
T=530 R, 540 R
V=100ft^3
@70F=530R
n=14.7*100/(10.7316*530)=.2585
mol wt=28.8
m=28.8*.2584=7.44 lb
@ 80f=540R
n=14.7*100/(10.7316*540)=.2537
m=.2537*28.8=7.31 lb

Anonymous2006-11-23T11:42:18Z

Air consists of approx. 79%N2 and 21%O2.
Mol. wt = O.79 x 28 + 0.21 x 32 = 28.84 g/ mol

Therefore, mass per liter = 28.84/ 22.40 = 1.288 g at STP

(Note that in the answer I have only recorded 3 decimal points, ie 1 mg. Greater accuracy is unnecessary and confusing)

Anonymous2006-11-23T11:29:37Z

70 degrees F, 100 ft3 = 7.50 lbs approx
80 degrees F, 100 ft3 = 7.35 lbs approx

Anonymous2006-11-23T10:03:18Z

I think air ways Gravity

Jim Burnell2006-11-23T09:45:30Z

You should be able to calculate it pretty easy with the density values from this website:

http://www.engineeringtoolbox.com/air-desity-specific-weight-d_600.html

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