How many moles of pcl5 can be produced from 28.0 g of p4 (and excess cl2) ?

P₄ + 10Cl₂ - - - > 4PCl₅

stoichiometry of P₄ to PCl₅ is 1:4

number of moles of P₄ reacted - 28.0 g / 124 g/mol = 0.22 mol

Cl₂ is in excess therefore P₄ is the limiting reactant, amount of product formed depends on amount of limiting reactant present

according to molar ratio of 1:4

number of PCl₅ moles formed - 0.22 mol x 4 = 0.88 mol

0.88 mol of PCl₅ is formed