big test today i need help

Question

The reaction of chlorine gas with solid phosphorus (P₄) produces solid phosphorus pentachloride. When 35.5 g of chlorine reacts with 4.13 g of P_4.

a. Balance the equation

      Cl₂ +   P₄ →  PCl₅

b. Which reactant is limiting?  (Cl₂ or P₄)

c. Which reactant is in excess?   (Cl₂ or P₄)

Answer 1

1 mol of Cl has mass 35.453 g

So 1 mol of Cl₂ has mass 2 x 35.453 = 70.906 g

So we have 35.5 / 70.906 = 0.501 moles of Cl₂

1 mol of P has mass 30.97 g

1 mol of P₄ has mass 4 x 30.97 = 123.88 g

We have 4.13 / 123.88 = 0.03 moles of P₄

From the equation we need equal numbers of moles of each to react together

Therefore as 0.03 < 0.501 the P₄ is limiting, and the Cl₂ is in excess

[ so all the P₄ will react , and 0.501 - 0.03 = 0.471 moles of Cl₂ will not react]