StoichiometryStoichiometry

Proportional Proportional RelationshipsRelationships

I have 5 eggs. How many cookies can I make?

3/4 c. brown sugar1 tsp vanilla extract2 eggs2 c. chocolate chipsMakes 5 dozen cookies.

2 1/4 c. flour1 tsp. baking soda1 tsp. salt1 c. butter3/4 c. sugar

5 eggs 5 doz.2 eggs

= 12.5 dozen cookies

Ratio of eggs to cookies

x

Proportional Proportional RelationshipsRelationships

StoichiometryStoichiometry• mass relationships between

substances in a chemical reaction• based on the mole ratio

Mole RatioMole Ratio• indicated by coefficients in a

balanced equation

2 Mg + O2 Mg + O22 2 MgO 2 MgO

Stoichiometry StepsStoichiometry Steps1. Write a balanced equation.2. Identify known & unknown.3. Line up conversion factors.

• Mole ratio - moles moles• Molar mass - moles grams

4. Cancel units.5. Multiply across top & bottom.6. Final divide.

Stoichiometry ProblemsStoichiometry Problems

How many moles of KClO3 must decompose in order to produce 9 moles of oxygen gas?

9 mol O2 2 mol KClO3

3 mol O2

= 6 mol KClO3

2KClO3 2KCl + 3O2 ? mol 9 mol

x

Stoichiometry ProblemsStoichiometry ProblemsHow many grams of CuO are

needed to produce 4 moles H2O?

4 mol H2O

79.55 g CuO

1 molCuO

= 318.2 g CuO

CuO + 2HCl CuCl2 + H2O ? g 4 moles

1 molCuO

1 molH2O

x x

Stoichiometry ProblemsStoichiometry ProblemsHow many grams of silver will be

formed from 12.0 g copper?

12.0g Cu

107.87 g Ag

1 molAg

= 40.7 g Ag

Cu + 2AgNO3 2Ag + Cu(NO3)2 12.0 g ? g

2 molAg

1 molCu

1 molCu

63.55g Cu

x x x

Stoichiometry ProblemsStoichiometry ProblemsHow many grams of ammonia will

be formed from 5.40 g of hydrogen?

5.40g H2

17.04 g NH3

1 molNH3

= 30.37 g NH3

N2 + H2 NH3 5.40 g ? g

2 molNH3

3 molH2

1 molH2

2.02g H2

x x x

3 2