1. LR/ER/Theoretical Yield/Percent Yield
Ch. 9 Conversions
LR/ER/Theoretical Yield/Percent Yield
Kierston Margetts

2. Chapter Vocabulary / Topics
Limiting Reactant- what you run out of first
Excess Reactant- what you have left over
Theoretical Yield- what you should make according to the math
Percent Yield- percentile comparison between experimental yield and theoretical yield

3. Real Life Problems
Cooking recipes are comparable to chemical equations
3 cups flour + 1 stick butter + 2 cups sugar + 1 can pumpkin → 2 pumpkin pies
(available ingredients: 80 cups flour, 17 sticks butter, 65 cups sugar, 20 cans pumpkin)
Always find limiting reactant first
Do this with each ingredient, the ingredient that makes the least # of pies is the Limiting reactant.
80 cups flour pies X
= 53 pies
3 cups flour

4. Real Life Problems Cont.
With the limiting reactant you can now find the excess of each ingredient
Subtract this number from given number in available ingredient list
You can also find the % yield
Amount of LR available Amt. of excess ingredient used in eqn
Amt. of LR used in eqn X
Actual # of pies made
Theoretical # of pies made
X 100

5. Chemical Problems
Grams A → Mol A → Mol B → Grams B

6. How to Find the LR of Chemical Problems
50.0 g Al₂(SO₄)₃ and CaCl₂
Al₂(SO₄)₃ (aq) + 3CaCl₂ (aq) → 2AlCl₃ (aq) + 3CaSO₄ (s) g
gR₁ → gP₁
gR₂ → gP₁

7. How to Find the LR of Chemical Problems
50.0 g Al₂(SO₄)₃ mol Al₂(SO₄)₃ mol AlCl₃ g AlCl₃ X X X
g Al₂(SO₄)₃ 1 mol Al₂(SO₄)₃ mol AlCl₃
= 38.9 g AlCl₃
100. g CaCl₂ mol CaCl₂ mol AlCl₃ g AlCl₃ X X X
g CaCl₂ mol CaCl₂ mol AlCl₃
= 80.1 g AlCl₃

8. How to Find Amount of Excess Reactant Left Over
Al₂(SO₄)₃ (aq) + 3CaCl₂ (aq) → 2AlCl₃ (aq) + 3CaSO₄ (s)
gLR → gER used

9. How to Find Amount of Excess Reactant Left Over
50.0 g Al₂(SO₄)₃ mol Al₂(SO₄)₃ mol CaCl₂ g CaCl₂ X X X
g Al₂(SO₄)₃ mol Al₂(SO₄)₃ mol CaCl₂
= 48.7 g CaCl₂ used
100. g available g used = 51.3 g CaCl₂ left

10. How to Find Theoretical Yield
TIP: After reading the problem questions, if one question asks for the theoretical yield of a certain product, this should be the product you use to find the LR.
Process is the exact same as finding the LR
EX: the theoretical yield of AlCl₃ is 38.9 g

11. How to Find the Percent Yield
Actual (given in ?)
X 100
Theoretical

12. How to Find the Percent Yield
Question: If I make 35.0 g of AlCl₃ what is the percent yield?
35.0 g
38.9 g
X 100 = 89.9 %

13. How to find Joules
Al₂(SO₄)₃ (aq) + 3CaCl₂ (aq) → 2AlCl₃ (aq) + 3CaSO₄ (s) + 250kJ
50.0 g Al₂(SO₄)₃ mol Al₂(SO₄)₃ kJ J X X X
g Al₂(SO₄)₃ mol Al₂(SO₄)₃ kJ
gLR → energy
=36533 J