1. Stoichiometry
“In solving a problem of this sort, the grand thing is to be able to reason backward. This is a very useful accomplishment, and a very easy one, but people do not practice it much.”
Sherlock Holmes, in Sir Arthur Conan Doyle’s A Study in Scarlet

2. Review: Chemical Equations
Chemical change involves a reorganization of
the atoms in one or more substances.
C2H5OH + 3O2 ® 2CO H2O
reactants
products
When the equation is balanced it has quantitative significance:
1 mole of ethanol reacts with 3 moles of oxygen to produce 2 moles of carbon dioxide and 3 moles of water

3. What is Stoichiometry?
Stoichiometry is the study of quantitative relationships between the amounts of reactants used and the amounts of products formed by chemical reactions.
Chemical reactions stop when one reactant is used up.
Stoichiometry is based on the Law of Conversation of Mass

4. Particle and Mole Relationships
4 Fe (s) + 3 O2 (g)  2Fe2O3 (s)
Words?
Particles?
Moles?
Mass?
Total Reactants/Total Products?

5. Mole Ratios
A mole ratio is a ratio between the numbers of moles of any two substances in a balanced equation.
2Al(s) + 3Br2(l)  2AlBr3(s)
What is the mole ratio of Bromine to Aluminum?
What is the mole ratio of Aluminum Bromide to Bromine?
3:2

6. Stoichiometric Calculations
All stoichiometric calculations begin with a balanced chemical equation.
You could be asked to perform one of the following:
Solve Mole to Mole Problems
Solve Mole to Mass Problems
Solve Mass to Mass Problems
There are steps to help you!!!!

7. Calculating Masses of Reactants and Products
Balance the equation.
Convert mass or volume to moles, if necessary.
Set up mole ratios.
Use mole ratios to calculate moles of desired substituent.
Convert moles to mass or volume, if necessary.

8. Working a Stoichiometry Problem
6.50 grams of aluminum reacts with an excess of oxygen. How many grams of aluminum oxide are formed.
1. Identify reactants and products and write the balanced equation. 4 Al + 3 O2 2
Al2O3
a. Every reaction needs a yield sign!
b. What are the reactants?
c. What are the products?
d. What are the balanced coefficients?

9. Working a Stoichiometry Problem
6.50 grams of aluminum reacts with an excess of oxygen. How many grams of aluminum oxide are formed?
4 Al O2  2Al2O3
6.50 g Al
1 mol Al
2 mol Al2O3
g Al2O3 =
? g Al2O3
26.98 g Al
4 mol Al
1 mol Al2O3
12.3 g Al2O3

10. Limiting Reactant
The limiting reactant is the reactant
that is consumed first, limiting the amounts of products formed.