Phosphorus pentachloride is formed when 17.2 g of chlorine gas react with 23.2 g of solid phosphorus (p2). determine the reactant that is in excess.

The balanced equation for the above reaction is;
P₂ + 5Cl₂ ---> 2PCl₅
Stoichiometry of P₂ to Cl₂ is 1:5
Number of P₂ moles present - 23.2 g/ 62 g/mol = 0.37 mol
Number of Cl₂ moles present - 17.2 g/ 71 g/mol =0.24 mol
If Cl₂ is the limiting reactant, 
then number of P₂ moles that react with 0.24 mol of Cl₂ - 0.24/5 = 0.048 mol 
Only 0.048 mol of P₂ is needed, but 0.37 mol of P₂ is provided, therefore P₂ reactant is in excess.
Excess reactant is the reagent provided in excess and only a fraction of this amount is used up for the reaction.
An amount of 0.37 - 0.048 = 0.322 mol of P₂ is remaining after the reaction