1. Chapter 9 Mole Ratios Calculations with Equations Limiting Reactants Percent Yield 1

2. Mole Ratio Mole Ratio Shows the ratio between two of the substances in a balanced equation Derived from the coefficients in the equation 2

3. Writing Mole Ratios 4 Fe + 3 O 2 2 Fe 2 O 3 Fe and O 2 4 mol Feand3 mol O 2 3 mol O 2 4 mol Fe Fe and Fe 2 O 3 4 mol Feand2 mol Fe 2 O 3 2 mol Fe 2 O 3 4 mol Fe O 2 and Fe 2 O 3 3 mol O 2 and2 mol Fe 2 O 3 2 mol Fe 2 O 3 3 mol O 2 3

4. Learning Check 3 H 2 (g) + N 2 (g) 2 NH 3 (g) A. A mol ratio for H 2 and N 2 is A) 3 mol N 2 B) 1 mol N 2 C) 1 mol N 2 1 mol H 2 3 mol H 2 2 mol H 2 B. A mol ratio for NH 3 and H 2 is A) 1 mol H 2 B) 2 mol NH 3 C) 3 mol N 2 2 mol NH 3 3 mol H 2 2 mol NH 3 4

5. Chemical Calculations 4 Fe + 3 O 2 2 Fe 2 O 3 How many moles of Fe 2 O 3 are produced when 6.0 moles O 2 react? 6.0 mol O 2 x mol Fe 2 O 3 = 4.0 mol Fe 2 O 3 mol O 2 5

6. Learning Check 2 4 Fe + 3 O 2 2 Fe 2 O 3 How many moles of Fe are needed to react with 12.0 mol of O 2 ? 1) 3.00 mol Fe 2) 9.00 mol Fe 3) 16.0 mol Fe 6

7. Learning Check 4 Fe + 3 O 2 2 Fe 2 O 3 How many grams of O 2 are needed to produce 0.400 mol of Fe 2 O 3 ? 1) 38.4 g O 2 2) 19.2 g O 2 3) 1.90 g O 2 7

8. Calculating Mass of A Substance Balance equation Convert starting amount to moles Use coefficients to write a mole ratio Convert moles of desired to grams 8

9. Example and steps The reaction between H 2 and O 2 produces 13.1 g of water. How many grams of O 2 reacted? Write the equation H 2 (g) + O 2 (g)H 2 O (g) Balance the equation 2 H 2 (g) + O 2 (g)2 H 2 O (g) 9

10. Plan Setup g H 2 O mol H 2 O mol O 2 g O 2 13.1 g H 2 O x 1 mol H 2 O x 1 mol O 2 x 32.0 g O 2 18.0 g H 2 O 2 mol H 2 O 1 mol O 2 = 11.6 g O 2 10

11. Learning Check How many O 2 molecules will react with 505 grams of Na to form Na 2 O? 4 Na + O 2 2 Na 2 O Complete the set up: 505 g Na x 1 mol Na x ________ x _______ 23.0 g Na 11

12. Learning Check Acetylene gas C 2 H 2 burns in the oxyactylene torch for welding. How many grams of C 2 H 2 are burned if the reaction produces 75.0 g of CO 2? 2 C 2 H 2 + 5 O 2 4 CO 2 + 2 H 2 O 75.0 g CO 2 x _______ x _______ x _______ 12

13. Textbook practice Bookwork Pages 306, 308, 309, 311 (all problems) 9.2 section review ◦p.311 (#1-5) 13

14. Percent Yield You prepared cookie dough to make 5 dozen cookies. The phone rings while a sheet of 12 cookies is baking. You talk too long and the cookies burn. You throw them out (or give them to your dog.) The rest of the cookies are okay. How many cookies could you have made (theoretical yield)? How many cookies did you actually make to eat? (Actual yield) 14

15. Vocabulary Actual yield is the amount of product actually recovered from an experiment Theoretical (possible) yield is the maximum amount of product that could be produced from the reactant. Percent Yield is the actual yield compared to the maximum (theoretical yield) possible. 15

16. Percent Yield Practice 1. Write the equation for the reaction of iron (III) phosphate with sodium sulfate to make iron (III) sulfate and sodium phosphate. a.If you perform this reaction with 25 grams of iron (III) phosphate and an excess of sodium sulfate, how many grams of iron (III) sulfate can you make? b.If 18.5 grams of iron (III) sulfate are actually made when you do this reaction, what is your percent yield? c.Is the answer from b) reasonable? Explain. d.If you do this reaction with 15 grams of sodium sulfate and get a 65.0% yield, how many grams of sodium phosphate will you make? 16

17. Limiting Reactants If the amounts of two reactants are given, the reactant used up first determines the amount of product formed. Analogy: Suppose you are preparing cheese sandwiches. Each sandwich requires 2 pieces of bread and 1 slice of cheese. If you have 4 slices of cheese and 10 pieces of bread, how many cheese sandwiches can you make? 17

18. Learning Check How many sandwiches can you make? ____ slices of bread + ____ slices of cheese = ____ sandwiches What is left over? ________________ What is the limiting reactant? 18

19. Hints for LR Problems 1. For each reactant amount given, calculate the moles (or grams) of a product it could produce. 2.The reactant that produces the smaller amount of product is the limiting reactant. 3. The number of moles of product produced by the limiting reactant is ALL the product possible. There is no more limiting reactant left. 19