I. Stoichiometric

Calculations

The Big Kahuna

I. Stoichiometric

Calculations

The Big Kahuna

StoichiometryStoichiometry

StoichiometryStoichiometryStoichiometryStoichiometry

Greek stiocheion – element

metron – measure

Proportional Proportional RelationshipsRelationshipsProportional Proportional RelationshipsRelationships

Stoichiometry is all about proportional relationships. Certain amounts of ingredients are needed to make certain amounts of food or other things.

In our case, the ingredients are the reactants and the food is the products.

A. Proportional A. Proportional RelationshipsRelationshipsA. Proportional A. 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

1 stick + 2 gloves = 1 player

2 sticks:

8 gloves:

5 gloves:

needs 4 gloves to make 2 players

needs 4 sticks to make 4 players

makes 2.5 players

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

We can read this in several ways:

1. For every 1 mole of oxygen used, 2 moles of magnesium oxide are formed.

2. For every 2 moles of magnesium used, 1 mole of oxygen is required.

Come up with two similar sentences to these ones that are also true.

2 Mg + O2 Mg + O22 2 MgO 2 MgO2 Mg + O2 Mg + O22 2 MgO 2 MgO

B. Stoichiometry StepsB. Stoichiometry StepsB. Stoichiometry StepsB. Stoichiometry Steps

1. Write a balanced equation.2. Identify known & unknown.3. Determine conversion factors.

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

Core step in all stoichiometry problems!!

4. Calculate unknown

C. Stoichiometry C. Stoichiometry ProblemsProblemsC. Stoichiometry C. Stoichiometry ProblemsProblems

Ex 1) 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

Ex 2) How many grams of silver will be formed from 12.0 g copper?

Cu + 2AgNO3 2Ag + Cu(NO3)2 sm = 12.0 g mass = ?

# moles Cu =mm

sm

# moles Cu =63.54 g/mol

12.0 g

# moles Cu = 0.189 mol

# moles Ag = 0.378 mol

mass Ag = (0.378 mol) (107.87 g/mol)

mass Ag = 40.77 g

mass Ag = (# mol) (mm)

Ex 3) If you dropped 75.0 g of aluminum into sulfuric acid, how many grams of

hydrogen gas would be produced?

2Al + 3 H2SO4 Al2(SO4)3 + 3H2

sm = 75.0 g mass = ?

# moles Al =mm

sm

# moles Al =26.98 g/mol

75.0 g

# moles Al = 2.78 mol

# moles H2 = 4.17 mol

mass H2 = (# mol) (mm)

mass H2 = (4.17 mol)(2.016 g/mol)

mass H2 = 8.41 g

AssignmentAssignmentAssignmentAssignment

1. Stoichiometry: Mass-Mass problems from the workbook.