1. Introduction to Stoichiometry
Chapter 12
Introduction to Stoichiometry

2. How many S’mores can you make with the ingredients at hand?
Makin’ S’mores
Recipe
1 roasted marshmallow
2 graham cracker squares
1 chocolate
1 MM + 2 GC + 1 CH
1 s’more
How many S’mores can you make with the ingredients at hand?

3. Chocolate Chip Cookies!!
1 cup butter
1/2 cup white sugar
1 cup packed brown sugar
1 teaspoon vanilla extract
2 eggs
2 1/2 cups all-purpose flour
1 teaspoon baking soda
1 teaspoon salt
2 cups semisweet chocolate chips
Makes 3 dozen
How many eggs are needed to make 3 dozen cookies?
How much butter is needed for the amount of chocolate chips used?
How many eggs would we need to make 9 dozen cookies?
How much brown sugar would I need if I had 1 ½ cups white sugar?

4. Cookies and Chemistry…Huh!?!?
Just like chocolate chip cookies have recipes, chemists have recipes as well
Instead of calling them recipes, we call them reaction equations
Furthermore, instead of using cups and teaspoons, we use moles
Lastly, instead of eggs, butter, sugar, etc. we use chemical compounds as ingredients

5. Chemistry Recipes
Looking at a reaction tells us how much of something you need to react with something else to get a product (like the cookie recipe)
Be sure you have a balanced reaction before you start!
Example: 2 Na + Cl2  2 NaCl
This reaction tells us that by mixing 2 moles of sodium with 1 mole of chlorine we will get 2 moles of sodium chloride
What if we wanted 4 moles of NaCl? 10 moles? 50 moles?

6. Flow Chart Grams (given) Moles (given) Moles (Wanted) Grams (Wanted)
Divide by molar mass of given
Multiply by Molar Ratio
Multiply by molar mass of wanted

7. 2 HCl + Cu  CuCl2 + H2
Want
How many grams of hydrogen are produced when g of hydrochloric acid are reacted with copper?
Given

8. 2 NaClO3  2NaCl2 + 3O2
Want
How many moles of sodium chloride are produced in the decomposition reaction of grams of sodium chlorate?
Given

9. N2 + 3 H2  2NH3
Want
How many moles of hydrogen are needed to completely react with two moles of nitrogen?
Given

10. C6H12O6(aq)  2 C2H5OH(aq) + 2 CO2(g)
STOICHIOMETRY!
The fermentation of glucose (C6H12O6) produces ethyl alcohol (C2H5OH) and CO2:
C6H12O6(aq)  2 C2H5OH(aq) + 2 CO2(g)
How many moles of CO2 are produced when mol of C6H12O6 reacts in this fashion?
How many grams of C6H12O6 are needed to form g of C2H5OH?
How many grams of CO2 form when 7.50 g of C2H5OH are produced?

11. Limiting Reactant: Cookies
1 cup butter
1/2 cup white sugar
1 cup packed brown sugar
1 teaspoon vanilla extract
2 eggs
2 1/2 cups all-purpose flour
1 teaspoon baking soda
1 teaspoon salt
2 cups semisweet chocolate chips
Makes 3 dozen
If we had the specified amount of all ingredients listed, could we make 4 dozen cookies?
What if we had 6 eggs and twice as much of everything else, could we make 9 dozen cookies?
What if we only had one egg, could we make 3 dozen cookies?

12. Limiting Reactant
Most of the time in chemistry we have more of one reactant than we need to completely use up other reactant.
That reactant is said to be in excess (there is too much).
The other reactant limits how much product we get. Once it runs out, the reaction s. This is called the limiting reactant.

13. 2 Al(OH)3(s) + 3 H2SO4(aq)  Al2(SO4)3(aq) + 6 H2O(l)
Aluminum hydroxide reacts with sulfuric acid as follows:
2 Al(OH)3(s) + 3 H2SO4(aq)  Al2(SO4)3(aq) + 6 H2O(l)
( g/mol) ( g/mol) ( g/mol) (18.01 g/mol)
Which reagent is the limiting reactant when g Al(OH)3 and g H2SO4 are allowed to react? How many grams of Al2(SO4)3 can form under these conditions?

14. Limiting Reactant: Recap
You can recognize a limiting reactant problem because there is MORE THAN ONE GIVEN AMOUNT.
Convert ALL of the reactants to the SAME product (pick any product you choose.)
The lowest answer is the correct answer.
The reactant that gave you the lowest answer is the LIMITING REACTANT.
The other reactant(s) are in EXCESS.
To find the amount of excess, subtract the amount used from the given amount.
If you have to find more than one product, be sure to start with the limiting reactant. You don’t have to determine which is the LR over and over again!

15. Yields
The amount of product calculated to form when all of the limiting reagent reacts is called the theoretical yield.
The percent yield is related to the actual yield (what was actually recovered) and the theoretical yield (what could have been recovered in a perfect world).

16. Yields 2 H2(g) + CO(g)  CH3OH(l)
What is the percent yield of the following reaction if the manufacturer obtains 21.4 g of CH3OH from 8.0 g of H2 in the presence of 25 g CO?
2 H2(g) + CO(g)  CH3OH(l)
REMEMBER:
Equations must be balanced
Theoretical yield must be based on limiting reagent