Hey there!
theoretical yield = (87* 100 ) / 60 = 145 g of phosphorous pentachloride
the reaction for this process is :
molar mass P2O5 => 239.2125 g/mol
molar mass P4 => 123.90 g/mol
molar mass Cl2 => 70.9060 g/mol
P4 + 5 Cl2 --------------> 2 P2Cl5
moles of P2O5 :
145 g / 239.2125 => 0.6062 moles of P2O5
Therefore:
moles of P4 = 0.6062 mol / 2 => 0.3031 moles
moles of Cl2 = 5/2 * 0.6062 mol = 1.5154 moles
mass of P4 ( phosphours ) = 0.3031 mol * 123.90 => 37.554 grams
mass of Cl2 ( chlorine ) = 1.5154 mol * 70.9060 => 107.45 grams
Hope That helps!