1. Percent Yield and Limiting Reactants
Unit 9

2. Percent Yield
The percent yield is the percentage of a certain product actually produced in a chemical reaction.
The theoretical yield is predicted by a stoichiometry problem.

3. A. Percent Yield
measured in lab
calculated on paper

4. A. Percent Yield
When 45.8 g of K2CO3 react with excess HCl, 46.3 g of KCl are formed. Calculate the theoretical and % yields of KCl.
K2CO3 + 2HCl  2KCl + H2O + CO2
45.8 g
? g
actual: 46.3 g

5. A. Percent Yield K2CO3 + 2HCl  2KCl + H2O + CO2 45.8 g ? g
actual: 46.3 g
Theoretical Yield:
45.8 g
K2CO3
1 mol
K2CO3 g
2 mol
KCl
1 mol
K2CO3
74.55
g KCl
1 mol
KCl
= 49.4
g KCl

6. A. Percent Yield K2CO3 + 2HCl  2KCl + H2O + CO2 45.8 g 49.4 g
actual: 46.3 g
Theoretical Yield = 49.4 g KCl
46.3 g
49.4 g
% Yield =
 100 =
93.7%

7. Percent Yield
The reaction between SO2 and oxygen yields SO3.. Calculate the percent yield of SO3 if 40.0 grams of SO3is formed, when 32 grams of SO2 react with an excess of oxygen.
SO2 + O2  SO3
2SO2 + O2  2SO3

8. B. Limiting Reactants Available Ingredients Limiting Reactant
4 slices of bread
1 jar of peanut butter
1/2 jar of jelly
Limiting Reactant
bread
Excess Reactants
peanut butter and jelly

9. B. Limiting Reactants Limiting Reactant Excess Reactant
used up in a reaction
determines the amount of product
Excess Reactant
added to ensure that the other reactant is completely used up
cheaper & easier to recycle

10. B. Limiting Reactants 1. Write a balanced equation.
2. For each reactant, calculate the amount of product formed.
3. Smaller answer indicates:
limiting reactant
amount of product

11. Limiting Reactant Steps (version 2)
Step one
Write and balance the equation for the reaction.
Step two
Convert known masses to grams of product.
Step three
Determine limiting reactant and amount that can be made.
Step four
Determine the grams of excess from limiting reactant.

12. B. Limiting Reactants Zn + 2HCl  ZnCl2 + H2 79.1 g ? L 0.90 L 2.5M
79.1 g of zinc react with 0.90 L of 2.5M HCl. Identify the limiting and excess reactants. How many liters of hydrogen are formed at STP?
Zn HCl  ZnCl H2
79.1 g
0.90 L
2.5M
? L

13. A. Limiting Reactants Zn + 2HCl  ZnCl2 + H2 79.1 g 0.90 L 2.5M ? L
g Zn
1 mol Zn
65.39
g Zn
1 mol H2 Zn
22.4 L H2
1 mol
= 27.1 L H2

14. A. Limiting Reactants Zn + 2HCl  ZnCl2 + H2 79.1 g 0.90 L 2.5M ? L
2.5 mol
HCl
1 L
1 mol H2
2 mol
HCl
22.4
L H2
1 mol H2
= 25 L H2

15. A. Limiting Reactants Limiting reactant: HCl Excess reactant: Zn
Zn: 27.1 L H2
HCl: 25 L H2
Limiting reactant: HCl
Excess reactant: Zn
Product Formed: 25 L H2
left over zinc

16. Limiting Reagent or Reactant 2 (problem #2)
How many grams of ammonia will be produced when 20.0 grams of potassium hydroxide react with 15.0 grams of ammonium sulfate?
Step 1
2KOH + (NH4)2SO4  K2SO4 +2NH3 +2H2O

17. (NH4)2SO4 is the limiting reagent because it will make the least amount of product. It is the reactant that will run out first.

18. Limiting Reagent or Reactant 2