1.44x10^23 molecules of oxygen gas
The ideal gas law is
PV = nRT
where
P = pressure (800.0 Torr)
V = volume (5.60 L)
n = number of moles
R = Ideal gas constant (62.363577 L*Torr/(K*mol) )
T = absolute temperature (27C + 273.15 = 300.15 K)
Let's solve for n, the substitute the known values and solve.
PV = nRT
PV/RT = n
(800.0 Torr*5.60 L)/(62.363577 L*Torr/(K*mol)*300.15 K) = n
(4480 L*Torr)/(18718.42764 L*Torr/mol) = n
0.239336342 mol = n
So we have 0.239336342 moles of oxygen molecules. To get the number of atoms, we need to multiply by avogadro's number, so:
0.239336342 * 6.0221409x10^23 = 1.44x10^23
