1. Stoichiometry

2. Review of Molar Mass
The molar mass (MM) of a compound is all the atomic masses for the molecule (or compound) added up.
Ex. Molar mass of CaCl2
Avg. Atomic mass of Calcium = 40.08g
Avg. Atomic mass of Chlorine = 35.45g
Molar Mass of calcium chloride = g/mol Ca + (2 X 35.45) g/mol Cl  g/mol CaCl2 20
Ca 
17 Cl 35.45

3. Practice Ca3(PO4)2 Calculate the Molar Mass of calcium phosphate
Formula =
Masses elements:
Ca = 40, P = 31, O = 16,
Molar Mass = 3x40 + 2x31 + 8x16
= 310 g/mol
Ca3(PO4)2

4. Everything must go through Moles!!!
Calculations
molar mass Avogadro’s number Grams Moles particles
Everything must go through Moles!!!

5. 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
2 eggs
1 cup butter
What is the ratio of eggs to butter to make 3 dozen cookies?
What is the ratio of butter to chocolate chips?
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?
1 to 2

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

7. 4 moles of Na and 2 moles of Cl2
Chemistry Recipes
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
How much Na and Cl2 would be need if we wanted to make 4 moles of NaCl?
4 moles of Na and 2 moles of Cl2

8. Practice 50 mol H2 = 50 mol H2O (they have a 1:1 ratio)
Write the balanced reaction for hydrogen gas reacting with oxygen gas.
2 H2 + O2  2 H2O
What if we had 50 moles of hydrogen, how much oxygen would react with it?
How much water would be produced?
50 mol H2 x 1 mol O2 = 25 mol O2
2 mol H2
Mole ratio
50 mol H2 = 50 mol H2O (they have a 1:1 ratio)

9. Mole Ratios 5 moles Na 1 mol Cl2 2 mol Na = 2.5 moles Cl2
The mole ratio is used to switch between substances in a chemical equation.
Example: How many moles of chlorine are needed to react with 5 moles of sodium?
2 Na + Cl2  2 NaCl
5 moles Na 1 mol Cl2
2 mol Na
= 2.5 moles Cl2

10. Mole-Mole Conversions
How many moles of sodium chloride will be produced if 2.6 moles of chlorine gas reacts with excess sodium metal?
2 Na + Cl2  2 NaCl
2.6 moles Cl2 x 2 mol NaCl = 5.20 mol of NaCl
1 mol Cl2

11. Mole-Mass Conversions
Most of the time in chemistry, the amounts are given in grams instead of moles
Example: How many grams of chlorine are required to react completely with 5.00 moles of sodium to produce sodium chloride?
2 Na + Cl2  2 NaCl
Molar mass
Mole ratio
5.00 moles Na 1 mol Cl g Cl2
2 mol Na 1 mol Cl2
= 177g Cl2

12. Practice
Given Quantity  convert to moles  mole ratio  convert to final units
Calculate the mass in grams of Iodine required to react completely with 0.50 moles of aluminum.
2 Al + 3 I2  2 AlI3
0.50 moles Al
X 3 moles I2
2 moles Al
X g I2
moles
= g I2

13. Mass-Mole 10.0 g H2O 1 mol H2O 2 mol C2H6 18.0 g H2O 6 mol H20
We can also start with mass and convert to moles of product or another reactant
Calculate the number of moles of ethane (C2H6) needed to produce 10.0 g of water
2 C2H6 + 7 O2  4 CO2 + 6 H20
Convert to moles
Given quantity
Multiply by the Mole ratio
10.0 g H2O 1 mol H2O 2 mol C2H6
18.0 g H2O 6 mol H20
= mol C2H6

14. Consider : 4NH3 + 5O2  6H2O + 4NO
How many grams of H2O are produced if 1.9 mol of NH3 are combined with excess oxygen?
How many grams of O2 are required to produce 0.3 mol of H2O?
# g H2O=
6 mol H2O
4 mol NH3 x
18.02 g H2O
1 mol H2O x
51.4 g H2O =
1.9 mol NH3
# g O2=
5 mol O2
6 mol H2O x
32 g O2
1 mol O2 x
8 g O2 =
0.3 mol H2O

15. Mass-Mass Conversions
Most often we are given a starting mass and want to find out the mass of a product we will get (called theoretical yield) or how much of another reactant we need to completely react with it (no leftover ingredients!)
Given Quantity  convert to moles  mole ratio  convert to final units

16. Mass-Mass Conversion 2.00g N2 1 mol N2 2 mol NH3 17.06g NH3
Ex. How many grams of ammonia are produced when 2.00g of nitrogen react with excess hydrogen.
N2 + 3 H2  2 NH3
2.00g N mol N mol NH g NH3
28.02g N2 1 mol N mol NH3
= 2.4 g NH3

17. Practice: Grams to Grams
How many grams of calcium nitride are produced when 2.00 g of calcium reacts with an excess of nitrogen?
3 Ca + N2  Ca3N2
2.00 g Ca x 1 mole Ca x 1 mole Ca3N2 x 148 g Ca3N2 = 2.47 g Ca3N2
40 g mol Ca mole
Given amount  change to moles  multiply by the mole ratio  change to (put the one on top that you grams
are solving for)

18. Gases and Stoiochiometry
Avogadro's Hypothesis - at the same temperature and pressure equal volumes of gas have the same number of particles.
At STP 1 mole of any gas has a volume of 22.4 L
STP = 0ºC and 1 atmosphere pressure

19. Gases and Stoichiometry
2 H2O2 (l) ---> 2 H2O (g) + O2 (g)
Decompose 1.1 g of H2O2 in a flask with a volume of 2.50 L. What is the volume of O2 at STP?
Bombardier beetle uses decomposition of hydrogen peroxide to defend itself.

20. Gases and Stoichiometry
2 H2O2 (l) ---> 2 H2O (g) + O2 (g)
Decompose 1.1 g of H2O2 in a flask with a volume of 2.50 L. What is the volume of O2 at STP?
Solution
1.1 g H2O mol H2O mol O L O2
34 g H2O mol H2O mol O2
= 0.36 L O2 at STP
Molar volume

21. Gas Stoichiometry: Practice!
A. What is the volume at STP of 4.00 g of CH4?
4.00 g CH4 x 1 mole x 22.4 L = L of CH4
16 g mole
B. How many grams of CO2 are produced from the combustion of 20 grams CH4 at STP?
CH4 + 2 O2  CO H2O
20 g CH4 x 1 mole x 1 mole CO2 x L = 28 L CO2
16 g mole CH4 1 mole