Quote (daiblorules @ Feb 14 2014 01:32am)

look at the formula first. its already balanced and you see that for 2 moles aluminum on reactant side you produce 2 moles aluminum chloride as a product.
this means if you produce 8.7 mole aluminum chloride you reacted 8.7 mole aluminum (with chlorine, which is irrelevant for this question, it is assumed you have unlimited chlorine since they don't mention a chlorine amount in problem)
so 8.7 moles aluminum x 1 mole aluminum is 26.982 g aluminum.
8.7x 26.982 = 234.7 grams aluminum needed