Question

Atoms in 50dm³ chlorine at ATP

Answer 1

22.4 meters^3 /mol of Cl2
so 2 * Avagadro's number atoms / mol = 6.02*10^23 *2 = 12.04*10^23 atoms/mol
we have 50*10^-3 m^3
so
(50 * 10^-3 /22.4)*12.04*10^23

Answer 2

I assume you mean STP

Answer 3

oops. There are 22.4 L (22.4 dm^3) in a mole of gas @ STP and that isn't = 22.4 cubic meters.
So we have 50 dm^3 x 1 mol/22.4 dm^3 = 2.23 mols Cl2.
Then 6.02E23 molecules/mol x 2.23 mol = 13.4E23 molecules Cl2.
Then 13.4E23 molecules Cl2 x (2 atoms in Cl2/molecule Cl2) = 2 x 13.4E23 = ? Check my arithmetic.
On the ATP subject, there is STP, NTP, SATP, ISA and USSA. I would guess you may have meant SATP. All of my calculating above are for STP and although "standard conditions" should be standard they ARE NOT. Since 1982 we are supposed to used 1 bar for pressure and not 1 atm. But MOST of the work I see, and even texts written much after 1982 still are using 1 atm for the standard. To complicate matters there are certain professional groups that use 20 C and not 0 C for standard T. My calculating above is based on 22.4 L/mol. If you want to convert to the newer 1 bar for pressure you can multiply my numbers above once you've checked them, by my number x (22.7/22.4)