Chapter 9 – STOICHIOMETRY

The MATH of a CHEMICAL REACTION

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

Example:

9.1 – Reaction Stoichiometry

      C2H6 +       O2       CO2 +       H2O

2 moles C2H6 reacts with 7 moles O2 to form 4 mole CO2 and 6 moles H2O

9.2 – Stoichiometry Calculations

-You need to be sure your units are canceling

-CAN ONLY SWITCH FROM ONE SUBSTANCE TO ANOTHER BY MOLES!!

9.2 – Stoichiometry Calculations

Types of Calculations:

1. mole of one substance to mole of another

Moles A Moles BRatio from Balanced

Equation

Example:4 NH3 + 3 O2 -> 2 N2 + 6 H2O

9.4 mole NH3 = ? mole N2

1. Rewrite the information given

2. Multiply

3. Draw a fraction line

4. DENOMINATOR IS THE SAME UNIT AS GIVEN

5. Set up numerator

6. Plug in known fraction numbers

7. Solve

Work:

More Practice:

9.2 – Stoichiometry Calculations

Types of Calculations:

2. mole of one substance to gram of another

Moles A Moles B

Ratio from Balanced Equation

Molar Mass from Periodic Table

Grams B

Example:4 NH3 + 3 O2 -> 2 N2 + 6 H2O

4.35 mole NH3 = ? g H2O

Work:

More Practice:

9.2 – Stoichiometry Calculations

Types of Calculations:

3. gram of one substance to mole of another

Grams A Moles A

Ratio from Balanced Equation

Molar Mass from Periodic Table

Moles B

Example:4 NH3 + 3 O2 -> 2 N2 + 6 H2O

19.3 g NH3 = ? mol O2

Work:

More Practice:

9.2 – Stoichiometry Calculations

Types of Calculations:

4. gram of one substance to gram of another

Grams A

Moles A

Ratio from Balanced Equation

Molar Mass from Periodic Table

Moles B

Grams B

Molar Mass from Periodic Table

Example:4 NH3 + 3 O2 -> 2 N2 + 6 H2O

18.6 g O2 = ? g N2

Work:

More Practice:

More Practice:

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”

Examples:-Making a Bicycle:

Limiting Reactants

1 2

1

1++

frame tires handlebars bike1 + 2 +

1

1

Stockroom Inventory: 10 18 13

Limiting Reactants

Examples:-Making a Bicycle: How many bikes can we make???

1 2

1

1++

frame tires handlebars bike1 + 2 +

1

1

10 18 13

How many bikes COULD we make from each component?

10 139

How many maximum could be made??

Limiting Reactants

9*We picked the smallest value of the “could make” answers!!

Which was the limiting reactant?? tires

What are the excess reactants?? frames and handlebars

Now a Chemistry Example:

Limiting Reactants

3Fe + 4H2O -> Fe3O4 + 4H2

Starting materials:

24 g Fe and 20 g H2O

How many moles / How many grams Fe3O4 will be produced?

Work:

Limiting Reactants

Fe2O3 + 3CO -> 2Fe + 3CO2

19.2 g Fe2O3 and 21.5 g CO

How many grams of iron will be formed?

Percent Yield

Compares the amount actually received in lab to the amount that was expected.

Actual Yield = The amount actually obtained

Theoretical Yield = The amount expected. The number you calculate with pen and paper.

% Yield = actual yieldx 100

theoretical yield

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

Percent Yield

Work:

3Fe + 4H2O -> Fe3O4 + 4H2

14.2 g Fe

27.8 g H2O

% Yield