1. Stoichiometry

2. What is Stoichiometry?
Stoichiometry: the study of quantitative relationships between amounts of reactants used and amounts of products formed. Stoichiometry is based on the Law of Conservation of Mass.
Stoichiometry allows us to determine the amount of substance that is consumed or produced by a reaction.
Ex: Consider the equation
C3H8 + 5O H2O + 3CO :5:4:3
We can “read” the molar ratios of the reactants and products. In this way, we can determine how many moles of O2 are needed to produce a precise amount of CO2.

3. How do we use Stoichiometry?
How much cake do you need? Stoichiometry allows us to make the right amount of product.

4. Does this seem right?
If we want to make 4 s’mores, we will need to have the proper amounts of all ingredients.

5. Stoichiometry in action
Here are the proper ratios of the ingredients.

6. Pair Work: Make a Poster
With a partner make a list of at least 4 ways you use stoichiometry.
Create an illustrated stoichiometry problem. (Use color, make it pop!)
Provide a complete answer to your stoichiometry problem.
Vote for the poster you think is best from the completed posters.

7. Molar Ratios
The coefficients give us the molar ratios of the reactants and products. Ex: 2Na + 1Cl2 2NaCl Molar ratio of Na:Cl is 2:1 Molar ratio of Na:NaCl is 1:1

8. Learning Check C3H8 + 5O2 4H2O + 3CO2
How many moles of O2 are needed per C3H8 for the reaction above?
How many moles of CO2 are produced for every mole of O2 that reacts?

9. Apply Stoichiometry to Recipes
Use the M&M Cookie recipe for the following problems:
Double the recipe
Triple the recipe
Halve the recipe
Adjust the recipe to make enough cookies for 20 people to have 5 cookies each
Adjust the recipe to make 210 cookies
Predict how many cookies you could make if you had a dozen eggs

10. Stoichiometry Calculations
We can convert grams to moles or moles to grams using molar masses. Ex: How many grams is 2 moles of H2O?

11. Stoichiometry Calculations
Begin by calculating the molar mass of H2O: Molar mass H2O = 2(1.008g/mol) H g/mol O g/mol H2O

12. Since we want to know the number of grams in 2 moles, we multiply the molar mass by 2 moles: (2mol)(18.015g/mol) = 36.03g H2O So 2 moles of H2O has a mass of grams.