1. Review – 1 More!
Propane (C3H8) and oxygen react to produce carbon dioxide and water.
Write AND BALANCE the chemical equation.
ANSWER: C3H8(g) + 5O2(g)→ 3CO2(g) + 4H2O
What type of reaction is this?
How many moles of each compound are represented?
How many grams of each compound are represented?

2. Law of Conservation of Mass
In every example, mass was conserved, meaning the mass of the reactants EQUALS the mass of the products!
While mass was equal on both sides of the equations, what was different?
ANSWER: number of molecules or number of moles

3. Assignment
Let’s look at Example Problem 12-1 on p.355. (This is the last equation we balanced.)
Notice how they write the equation “in terms of” molecules, moles, and mass.
Now do the Practice Problems on p.356

4. Mole Ratios
Def.: the ratio of the number of moles of any two substances in a balanced chemical equation.
Let’s look back at the 3 equations we balanced.
In the first one, we can identify several mole ratios:
4Fe/3O OR O2/4Fe
4Fe/2Fe2O3 OR Fe2O3/4Fe
3O2/2Fe2O3 OR Fe2O3/3O2

5. Mole Ratios, continued…..
What are the possible mole ratios for the other two example problems we worked?
Assignment: Practice Problems (p.357)