1. Chapter 9 – STOICHIOMETRY
The MATH of a CHEMICAL REACTION

2. 9.1 – Reaction Stoichiometry
-Ratio of compounds in a reaction
-YOU NEED A BALANCED CHEMICAL REACTION!!
Examples:
      Al +       O2 ®       Al2O3
What this means:
4 MOLES Al react with 3 MOLES O2 to form 2 MOLES Al2O3

3. 9.1 – Reaction Stoichiometry
Example:
      C2H6 +       O2 ®       CO2 +       H2O
2 moles C2H6 reacts with 7 moles O2 to form 4 mole CO2 and 6 moles H2O

4. 9.2 – Stoichiometry Calculations
-You need to be sure your units are canceling
-CAN ONLY SWITCH FROM ONE SUBSTANCE TO ANOTHER BY MOLES!!

5. 9.2 – Stoichiometry Calculations
Types of Calculations:
1. mole of one substance to mole of another
Ratio from Balanced Equation
Moles A
Moles B

6. Example: 4 NH3 + 3 O2 -> 2 N2 + 6 H2O 9.4 mole NH3 = ? mole N2
Rewrite the information given
Multiply
Draw a fraction line
DENOMINATOR IS THE SAME UNIT AS GIVEN
Set up numerator
Plug in known fraction numbers
Solve
Work:

7. More Practice:

8. 9.2 – Stoichiometry Calculations
Types of Calculations:
2. mole of one substance to gram of another
Ratio from Balanced Equation
Molar Mass from Periodic Table
Moles A
Moles B
Grams B

9. Example:
4 NH3 + 3 O2 -> 2 N2 + 6 H2O
4.35 mole NH3 = ? g H2O
Work:

10. More Practice:

11. 9.2 – Stoichiometry Calculations
Types of Calculations:
3. gram of one substance to mole of another
Ratio from Balanced Equation
Molar Mass from Periodic Table
Grams A
Moles A
Moles B

12. Example:
4 NH3 + 3 O2 -> 2 N2 + 6 H2O
19.3 g NH3 = ? mol O2
Work:

13. More Practice:

14. 9.2 – Stoichiometry Calculations
Types of Calculations:
4. gram of one substance to gram of another
Ratio from Balanced Equation
Molar Mass from Periodic Table
Molar Mass from Periodic Table
Grams A
Moles A
Moles B
Grams B

15. Example:
4 NH3 + 3 O2 -> 2 N2 + 6 H2O
18.6 g O2 = ? g N2
Work:

16. More Practice:

17. More Practice:

18. Limiting Reactants -Need a balanced equation!
-You will be given information about more than one starting material
-It is nearly impossible to add the perfect amount of both reactants
-Limiting Reactant = The reactant which will run out first
-Excess Reactant = The reactant which you have “more than enough of”

19. Limiting Reactants Examples: + + + + 10 18 13 1 1 1 2 1 2 1 1
-Making a Bicycle: 1 1 1 + 2 + + 1 + 2 1
frame
tires
handlebars 1
bike
Stockroom Inventory: 10 18 13

20. Limiting Reactants + 10 18 13 Examples:
-Making a Bicycle: How many bikes can we make??? 1 2 +
frame
tires
handlebars
bike 10 18 13
How many bikes COULD we make from each component? 13 10 9

21. 9 Limiting Reactants How many maximum could be made??
*We picked the smallest value of the “could make” answers!!
Which was the limiting reactant??
tires
What are the excess reactants??
frames and handlebars

22. Now a Chemistry Example:
Limiting Reactants
Now a Chemistry Example:
3Fe + 4H2O -> Fe3O4 + 4H2
Starting materials:
24 g Fe and 20 g H2O
How many moles / How many grams Fe3O4 will be produced?
Work:

23. Limiting Reactants
Fe2O3 + 3CO -> 2Fe + 3CO g Fe2O3 and 21.5 g CO How many grams of iron will be formed?

24. Percent Yield
Compares the amount actually received in lab to the amount that was expected.
Theoretical Yield = The amount expected. The number you calculate with pen and paper.
Actual Yield = The amount actually obtained
% Yield =

26. Percent Yield Example: 3Fe + 4H2O -> Fe3O4 + 4H2
Starting materials:
14.2 g Fe and 27.8 g H2O
After the experiment is complete:
17.3 g Fe3O4 are actually obtained

27. Percent Yield Work: 3Fe + 4H2O -> Fe3O4 + 4H2 14.2 g Fe 27.8 g H2O