1. Chapter 9: Stoichiometry
Modern Chemistry

2. What is stoichiometry
A combination of chemical reactions and mole calculations

3. Like a recipe…
2 cups sugar + 1 cup butter = 12 cookies How many cookies can I make with 5.5 cups of sugar? How many cups of butter will it take to make 125 cookies?

4. Balanced chemical reactions
Coefficients tell us the ratio of moles for each part of a reaction
Ratios can be used as conversion factors

5. Mole Ratio
A mole ratio is a conversion factor that relates the amounts in moles of any two substances involved in a chemical reaction
Example: 2Al2O3(l)  4Al(s) + 3O2(g)
Mole Ratios: mol Al2O3 2 mol Al2O mol Al
4 mol Al 3 mol O mol O2

6. Mg(s) + 2HCl(aq)  MgCl2(aq) + H2(g)
If 2 mol of HCl react, how many moles of H2 are obtained?
How many moles of Mg will react with 2 mol of HCl?
If 4 mol of HCl react, how many mol of each product are produced?
How would you convert from moles of substances to masses?

7. 2 Al2O3  4 Al + 3 O2 4 moles Al 3 moles O2 3 moles O2 4 moles Al
Write the possible mole ratios of aluminum to oxygen…
How many moles of oxygen are needed to react with 14.2 moles of aluminum?
4 moles Al
3 moles O2
3 moles O2
4 moles Al
14.2 mol Al
3 moles O2 =
10.7 mol O2
4 moles Al

8. Calculating

9. H2 + N2  NH3 27 moles H2 2 moles NH3 = 18moles NH3 3 moles H2
How many moles of NH3 can I make from 27 moles of hydrogen?
27 moles H2
2 moles NH3 =
18moles NH3
3 moles H2
Mole ratio

10. Moles aren’t practical, so…
We also use grams, particles, and liters in calculations
Remember, MUST BE IN MOLES to do the mole ratio conversion!!

11. More conversion factors
1 mole X = 6.02 E 23 atoms/molecules/f.units X
1 mole X = ______ grams X
1 mole X = 22.4 L X

13. Percent Yield
A measure of how much product is recovered in lab as compared to how much should have been theoretically produced

14. Cooking example Given 110 cookies Actual yield % yield = X 100 = 73%
If I use 25 cups of butter and make 110 cookies, what is my percent yield?
2 cups butter + 1 cup sugar  12 cookies
25 cups cookies
Given
110 cookies
Actual yield
% yield =
X 100
= 73%
Calculated yield
150 cookies
25 cups butter
12 cookies =
150 cookies
2 cups butter

15. Limiting Reagent
The amount of product formed depends on how much reactant you have
How many cookies can I make if I have 15 cups of sugar and 8.0 cups butter?
2 cups sugar + 1 cup butter  12 cookies
15 cups cups ? Cookies
**Do the problem twice
**Smaller product is the answer!

16. Chapter Review
Pg. 320
#’s 2-3, 5-7, 10-11, 14, , 26, 29