1. Stoichiometry
Section 12.1

2. What is Stoichiometry?
Study of quantitative relationships between amounts of reactants used and products formed.
Based on the Law of Conservation of Mass (Mass of the Reactants = Mass of the Products)
Ex. 4 Fe (s) + 3 O 2 (g)  2 Fe2O3 (s)

3. Ex. 2 Al (s) + 3 Br2 (l)  2 AlBr3 (s)
Mole Ratios
Ratio between the numbers of moles of any two substances in a balanced chemical equation.
Ex. 2 Al (s) + 3 Br2 (l)  2 AlBr3 (s)
Mole Ratios: 2 Al : 3 Br2
2 Al : 2 AlBr3
3 Br2: 2 AlBr3

4. Mole Ratio Practice
What mole ratios can be written for the decomposition of potassium chlorate?
2 KClO3 (s)  2 KCl (s) + 3 O2 (g)
Answer:
2 KClO3 : 2 KCl
2 KClO3 : 3 O2
2 KCl : 3 O2

5. Mole – Mole Conversions
The problem gives you moles and asks for moles as an answer
Balance the equation
Label the known substance (given in the problem) and the unknown substance (substance being asked for in the problem)
Determine the mole ratio that relates the known and unknown substances
Multiply the known number of moles by the mole ratio

6. (H) Mole – Mole Conversion Practice
2 K (s) + 2 H2O (l)  2 KOH (aq) + H2 (g)
How many moles of hydrogen are produced when mole of potassium is used?
Write the balanced equation
Given = mole K
Unknown = moles of H2
3. Write the mole ratio:
1 mole H2
2 mole K
Convert using: moles of known x moles of unknown
moles of known
Answer: x 1 mole H2 = mol H2
2 moles K

7. Stoichiometry Practice I (Mole-Mole Conversions)
H O2  H2O
8. How many moles of water can be produced with 6 moles of hydrogen?
9. How many moles of oxygen would be required to fully react with 8 moles of hydrogen?
10. How many moles of water can be produced with 4 moles of oxygen?
11. How many moles of hydrogen would be required to produced 10 moles of water?
12. How many moles of oxygen would be needed to produce 20 moles of water?

8. Mole – Mass Relationships
Coefficients in a balanced equation can be interpreted in
terms of representative particles and also by numbers of
moles of particles.
We can also use what we know about the conversion factor
that relates mass and number of moles to find the mass of
either the reactants or products.

9. How to solve mole to mass problems
Problem gives you moles and asks for mass as an answer
Balance equation
Label the known substance and the unknown substance
Determine the mole ratio that relates the known and unknown substances
Multiply the known number of moles by the mole ratio
Multiply the number of moles by the molar mass of the unknown substance

10. Mole – Mass Relationships
Ex. 4 Fe (s) + 3 O2 (g)  2 Fe2O3 (s)
4 mol Fe x 56 g Fe = 224 g Fe
1 mol Fe
3 mol O2 x 32 g O2 = 96 g O2
1 mol O2
Mass of Reactants = 320 g
2 mol Fe2O3 x 160 g Fe2O3 = 320 g
1 mol Fe2O3
Mass of Products = 320 g

11. Mass to Mass Relationships in Equations
Problem gives you mass and asks for mass as an answer
Balance equation
Label the known substance and the unknown substance
Convert from the mass to the moles
Use a mole ratio
Use the molar mass to convert from moles to mass

12. (CP) Mole – Mole Relationships in Equations Example
2 H2 + O2  2 H2O
How many moles of water can be produced with 6 moles of hydrogen?
Equation is balanced.
There are 2 moles of hydrogen, 1 mole oxygen, and 2 moles water.
6 H2 = x H2O 6 = x and 2x = 12
2 H H2O x = 6
4. X = 6 moles water

13. (CP) Mole – Mole Relationships in Equations
Balance the equation.
Coefficients = number of moles of each substance.
Use “x” for the “how many” compound.
Use ratio of moles given in problem to actual moles in equation.
Set up ratio.
Solve.

14. (CP) Mole to Mass Relationships in Equations
Balance the equation.
Coefficients = # of moles of each substance.
Use “x” for the “how many” compound.
Use ratio of moles given in problem to actual moles in equation.
Set up ratio and solve for “x”.
Multiply your answer by the molar mass of the element or compound you are trying to find.
(Example: Stoichiometry Practice I, # 4 at bottom)