1. Limiting Reactants and Excess
What is the Limiting Reagent (Reactant)?
It is the substance in a chemical reaction that runs out first.
The limiting reactant (reagent) determines how much product you can make.
If you are given amounts of more than one reactant, determine how much product you can make with each of them. Whichever produces the LEAST amount of product is your limiting reagent.

2. Practice Problems
Consider the reaction:
2 Al I2  2 AlI3
Determine the limiting reagent of the product, aluminum iodide, if one starts with:
a) moles of Al and 2.40 moles of iodine Al I2

3. Al is limiting reactant
1.20 moles of Al moles AlI moles AlI3
2 moles Al
2.40 moles I moles AlI moles AlI3
3 moles I2
Al is limiting reactant

4. What is the limiting Reactant with
1.20 grams of Al and 2.40 grams of iodine?
A 1.20g Al
B g I2
1.20 g Al 1mol Al mol AlI mols AlI3
g 2 mol Al
2.40 g I2 1 mol I mol AlI mols AlI3
g 3 mole I2
I2 is limiting Reactant! B

5. How many grams of excess reactant will remain?
2.40g I mol I mols Al g
g 3 mole I mol Al
g of Al reacted
Started with 1.20g g reacted
1.03 g in excess

6. 15.00 g aluminum sulfide and g of water react until the limiting reagent is used up. Here is the balanced equation for the reaction.
Al2S H2O  2 Al(OH) H2S
a.) What is the maximum mass of H2S which can be formed from these reagents ?
10.21g
11.35 g
15.00g Al2S mol Al2S mols H2S g
g mol Al2S mol H2S
10.21g H2S
12.00g H2O 1 mol H2O mols H2S g
18.008g mol H2O mol H2S
11.35g H2S
A g

7. What is the limiting Reactant?
A . H2O
B. Al2S3 B!
How much of the excess reactant is used up?
A, g
B g
C g
15.00g Al2S mol Al2S mols H2O g
g mol Al2S mol H20
10.84 g used up

8. Percent Yield Percent Yield = (Actual Yield / Theoretical Yield) * 100
Theoretical Yield is the amount that your stoichiometric calculations have predicted.
Actual Yield is what you actually produced in an experiment.

9. Example: In the reaction between nitrogen gas and hydrogen gas producing ammonia:
a.) If you start with 14 grams of N2 and 6.0 grams of H2, what will be the limiting reagent and the theoretical yield?
b.) If 10. grams of the product was formed, what would be the percent yield?