If you start with 4.5 moles of aluminum and 6.5 moles of copper chloride to make aluminum chloride and copper, what is the limiting reagent? 2AL+3CuCL->2ALCL3 + 3Cu

Copper chloride (CuCl) is the limiting reagent.

Explanation:

1) Balanced chemical equation (given):

2 Al + 3 CuCl → 2 Al Cl₃ + 3 Cu

2) Mole ratio:

2 mol Al : 3 mol CuCl ≈ 0.67 mol of Al per mol of CuCl

3) Starting ratio (given)

4.5 mol Al / 6.5 mol CuCl ≈ 0.69 mol Al per mol of CuCl

Since 0.69 > 0.67 means that you start with more Al atoms (4.5 moles) than what are needed to react with the given CuCl units (6.5 mol); i. e. when the 6.5 moles of CuCl are consumed, there will be an excess of Al, and the reaction will stop, because the CuCl is over, meaning the latter is the limiting reactant (it limits the yield).