Acknowledgement

1
Acknowledgement

• This is an adaptation of a presentation
  originally prepared by Mrs. Christy Johannesonn.
  I wish to thank Mrs. Johannesonn for sharing her
  work with teachers and students via her website.

2
Stoichiometry in the Real World

• Stoichiometry Ch. 12

3
A. Limiting Reactants

• Available Ingredients
• 4 slices of bread
• 1 jar of peanut butter
• 1/2 jar of jelly

• Limiting Reactant
• bread

• Excess Reactants
• peanut butter and jelly

4
A. Limiting Reactants

• Limiting 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

5
A. 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

6
A. Limiting Reactants

• 79.1 g of zinc react with 25.1g HCl. Identify the
  limiting and excess reactants. How many grams of
  zinc chloride are formed?

Zn 2HCl ? ZnCl2 H2
? g
79.1 g
25.1g
7
A. Limiting Reactants
Zn 2HCl ? ZnCl2 H2
? g
79.1 g
25.1g
79.1 g Zn
1 mol Zn 65.39 g Zn
1 mol ZnCl2 1 mol Zn
136.90g ZnCl2 1 mol ZnCl2
166g ZnCl2
8
A. Limiting Reactants
Zn 2HCl ? ZnCl2 H2
? g
79.1 g
25.1g
25.1g HCl
1 mol HCl 36.36g HCl
1 mol ZnCl2 2 mol HCl
136.90g ZnCl2 1 mol ZnCl2
47.3g ZnCl2
9
A. Limiting Reactants

• Enough Zn for 166g ZnCl2
• Enough HCl for 47.3g ZnCl2

Limiting reactant HCl Excess reactant
Zn Product Formed 47.3g ZnCl2
10
B. Percent Yield
11
B. 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
12
B. Percent Yield
K2CO3 2HCl ? 2KCl H2O CO2
45.8 g
? g
actual 46.3 g

• Theoretical Yield

45.8 g K2CO3
1 mol K2CO3 138.21 g K2CO3
2 mol KCl 1 mol K2CO3
74.55 g KCl 1 mol KCl
49.4 g KCl
13
B. Percent Yield
K2CO3 2HCl ?2KCl H2O CO2
45.8 g
49.4 g
actual 46.3 g

• Theoretical Yield 49.4 g KCl

X 100
93.7
Yield