The balanced chemical reaction is written as:
P4 + 10Cl2 = 4PCl5
To determine the moles of PCl5 produced, we use the initial amount of the limiting reactant which is P4 and the relation from the reaction. We do as follows:
22.0 g P4 ( 1 mol / 123.90 g ) ( 4 mol PCl5 / 1 mol P4 ) = 0.7103 mol PCl5 produced