HCl (g) + O2 Cl2 (g) + H2O (g)

Assuming that all the gases in this reaction are at STP, what number of molecules of hydrogen chloride gas are needed to completely react with oxygen to yield 50.00 mL of chlorine gas?

PV = nRT

Pressure times volume = number of moles times ideal gas constant times temperature

50mL =.05L

1 atm (.05) = n (.0821) (273)

.05 = n (22.4133)

.022 = n (number of moles)

6.022E23 molecules = 1 mole

.022 x 6.022E23 = 1.325E23 molecules