Let's assume ideal gas behavior for simplicity. We could use the equation below:
PV=nRT
Solve for n or the number of moles.
n = PV/RT = (3×10⁻³ atm)(1 L)/(0.0821 L·atm/mol·K)(250 K)
n = 1.462×10⁻⁴ moles ozone
For every 1 mole of any substance, Avogadro stipulated that there is an equivalent of 6.022×10²³ molecules. Thus,
# of ozone molecules = 1.462×10⁻⁴ mol * 6.022×10²³ molecules/1 mol
# of ozone molecules = 8.8×10¹⁹
