# Molecules In Air

1. Oct 3, 2004

### derekbeau

Air at STP has pressure p = 1 atm = 1.013 ×105 Pa, and temperature T = 273 K. Use the ideal gas law to determine the number of molecules in a cubic meter of air.

I have tried many different numbers and cant seem to get the correct answer. I guess I should use the formula

PV = NkT

so
P = 1 atm or 101.3 kPa? i tried both
V = 1 m^3 or 1000 L? also tried both
T = 273 K
k = 8.617385 x 10-5 eV/K?

so (101.3 kPa)(1000 L) = N (8.617385 x 10-5 eV/K)(273 K)

do you see what i am doing wrong?

Thanks

2. Oct 3, 2004

### Sirus

For these units, use k=universal gas constant=R=8.314. I forget the units, but they cancel properly for kPa, L, moles, and Kelvin in the formula. Also remember that when you find N, that is the amount in moles (you must convert to molecules).

3. Oct 3, 2004

### derekbeau

no, nRT would give me moles, NkT gives me molecules

4. Oct 3, 2004

### derekbeau

nvm you were right, i got wrong info off a webpage

thanks a ton