Stoichiometry
A. Proportional Relationships
2 1/4 c. flour
1 tsp. baking soda
1 tsp. salt
1 c. butter
3/4 c. sugar
3/4 c. brown sugar
1 tsp vanilla extract
2 eggs
2 c. chocolate chips
Makes 5 dozen cookies.
• I have 5 eggs. How many cookies
can I make?
Ratio of eggs to cookies
5 eggs 5 doz.
2 eggs
= 12.5 dozen cookies
A. Proportional Relationships
• Stoichiometry
– mass relationships between
substances in a chemical reaction
– based on the mole ratio
• Mole Ratio
– indicated by coefficients in a
balanced equation
2 Mg + O2  2 MgO
Use Mole Island and Stoich Cheat Sheet
B. Stoichiometry Steps
1. Write a balanced equation.
2. Identify the given and find.
3. Line up conversion factors.
•– Mole ratio - moles
molesmoles
moles
– Molar mass - moles  grams
– Molarity moles  liters soln
– Molar volume - moles  liters gas
Core step in all stoichiometry problems!!
4. Check sig figs, units & circle your
answer!
Conversion Factor
# Moles A
# Moles B
The #’s in front of A & B MUST come from
the balanced chemical equation
Mole – Mole Relationship
Fe + O2  Fe2O3
1. Balance
the reaction
2. Find the mole ratio of Iron to Oxygen
4 mol Fe / 3 mol O2
3. Find the mole ratio of Iron to Iron (III) oxide
4 mol Fe / 2 mol Fe2O3
4. Find the mole ratio it Oxygen to Iron (III) oxide
3mol O2 / 2 mol Fe2O3
Mole – Mole Relationship
How many moles of Fe2O3 will form from
5.0 mols of Fe?
5.0 mole Fe x 2 mol Fe2O3
4 mol Fe
2.5 mol Fe2O3
Mole – Mass Relationship
How many grams of NaCl will be
produced from 1.25 mol of chlorine gas
reacting with sodium?
1. What type of reaction is this? Write the
balanced equation.
2 Na + Cl2  2NaCl
Mole – Mass Relationship
2. Work the problem. Remember Mole
Ratio and Sigfigs!
1.25 mol Cl2 x 2 mol NaCl x 58.443 g NaCl
1 mol Cl2
1 mol NaCl
146 g NaCl
Mass to Mole Relationship
Fe3O4 + 4 CO  3 Fe + 4 CO2
How many moles of CO are needed to
react with 16.5 g of Fe3O4
Mass – Mass Relationships
Ammonium nitrate decomposes into
dinitrogen monoxide gas and water.
Determine the amount of water produced
if 25.0 g of ammonium nitrate
decomposes.
1. Write the balanced reaction
NH4NO3  N2O + 2 H2O
Mass – Mass Relationships
25.0 g NH4NO3 x 1 mol NH4NO3 x 2 mol H2O
x 18.0153 g H2O
80.0434 g NH4NO3 1 mol NH4NO3
1 mol H2O
11.3 g H2O