Stoichiometry involves using the mole ratios from a balanced chemical equation to calculate the quantities of reactants and products involved in a chemical reaction. There are four main types of stoichiometry problems involving moles to moles, moles to mass, mass to moles, and mass to mass. Solving these problems uses the mole ratios and molar masses of substances to convert between amounts in moles and grams. The limiting reagent is the reactant that limits the amount of product that can be formed, and the theoretical yield is calculated based on stoichiometry while the actual yield is measured experimentally. The percent yield compares the actual and theoretical yields.

1. Stoichiometry
From the Greek words
“stoicheion” meaning “element”
and “metron” meaning “measure”

2. Stoichiometry
• Involves the mass relationships between
reactants and products in a chemical reaction.
• All reaction stoichiometry relationships start
with a balanced chemical equation.
• Equation gives the relative numbers of moles
of reactants and products.

3. Stoichiometry
• Solve problems using RATIOS from the
balanced equation.

4. Mole Ratio
Ratios produced from the
balanced equation
2H2 + O2  2H2O
• Possible mole ratios:
• 2H2 2H2 1O2
1O2 2H2O 2H2
1O2 2H2O 2H2O
2H2O 2H2 1O2

5. Reaction Stoichiometry Problems
Type 1 – given/unknown = mole/mole
• Given and unknown quantities are amounts in
moles
Amount of given Amount of unknown
Substance (mol) substance (mol)

6. Reaction Stoichiometry Problems
Type 2 – given/unknown = mole/mass(g)
• Given quantity is amount in moles and
unknown quantity is amount in grams
Amount of givenAmount of unknown
Substance (mol) substance (grams)

7. Reaction Stoichiometry Problems
Type 3 – given/unknown = mass(g)/mole
• Given quantity is in grams, and unknown
quantity is amount in moles
Amount of givenAmount of unknown
Substance (grams) substance (mol)

8. Reaction Stoichiometry Problems
Type 4 – given/unknown = mass(g)/mass(g)
• Given and unknown quantities are amounts in
grams
Amount of givenAmount of unknown
Substance (grams) substance (grams)

9. Reaction Stoichiometry Problems
Solving mole-mole calculations
• Write down given quantity in moles
• Write mole ratio of unknown/given
• Multiply fractions (numerator x numerator;
denominator x denominator)
• Reduce any remaining fraction to a decimal number

10. Reaction Stoichiometry Problems
Solving mole to mass calculations
• Write down given quantity in moles
• Multiply by mole ratio of unknown/given
• Multiply fractions (numerator x numerator;
denominator x denominator)
• Reduce any remaining fraction to a decimal number
• Multiply by molar mass of unknown.

11. Reaction Stoichiometry Problems
Solving mass to mole calculations
• Write down given quantity in grams
• Divide by molar mass of given
• Multiply by mole ratio of unknown/given
• Multiply fractions (numerator x numerator;
denominator x denominator)
• Reduce any remaining fraction to a decimal number

12. Reaction Stoichiometry Problems
Solving mass-mass calculations
• Write down given quantity in grams
• Divide by molar mass of given
• Multiply by mole ratio of unknown/given
• Multiply fractions (numerator x numerator;
denominator x denominator)
• Reduce any remaining fraction to a decimal number
• Multiply by molar mass of unknown

13. Limiting Reagent
• Reactant which will LIMIT the amount of
product produced.
• Need to calculate amount of product for BOTH
given reactants to determine which limits the
reaction.
• The reagent left over is called the excess
reactant.

14. Theoretical Yield
Amount of product made under IDEAL
conditions.
The most possible product you can make.
Almost never happens.
This is the number you calculate using
stoichiometry.

15. Actual Yield
• Amount of product made during the actual
reaction in the laboratory.

16. Percent Yield
• Ratio of actual yield/theoretical yield
• Tells you how good your reaction really was.
• % yield = Actual yield X 100
Theoretical
Yield