1. Chap. 9: Stoichiometry Identify the mole ratio of any two species in a chemical reaction. Calculate theoretical yields from chemical equations.

2. Identify the mole ratio of any two species in a chemical reaction. How do you calculate the quantity of reactants and products in chemical reactions? The calculation of quantities in chemical reactions is called stoichiometry. Use the chemical equation to predict ratio of reactants and products N 2 +3H 2  2NH 3 1 molecule N 2 reacts with 3 molecules H 2 producing 2 molecules NH 3 1 mole N 2 reacts with 3 moles H 2 producing 2 moles NH 3 The balanced equations gives us the ratio in particles or moles (not mass) of the chemicals involved in the reaction. The ratio of N 2 to NH 3 is 1:2 The ratio of NH 3 to H 2 is 2:3 The ratio of H 2 to N 2 is 3:1

3. Identify the mole ratio of any two species in a chemical reaction. Consider the reaction: 2C 8 H 18 + 25O 2  16CO 2 + 18H 2 O What is the ratio of O 2 to CO 2 ? 25:16 What is the ratio of H 2 O to C 8 H 18 ? 18:2 What is the ratio of CO 2 to H 2 O? What is the ratio of O 2 to C 8 H 18 ? Remember these ratios are in particles or moles. We will be using moles.

4. Calculate theoretical yields from chemical equations. The Four Steps to Stoichiometric Enlightenment Step 1: Write the balanced chemical equation. Step 2: Convert the known chemical amount to moles If amount in grams: Divide by formula weight If amount in particles: Divide by 6.02E 23 Step 3: Ratio the unknown (top) to the known (bottom) molar quantities. From Problem From Balanced Equation X moles of given (known) x Coefficient of Unknown = moles of unkown Coefficient of Known Step 4: Convert molar quantity from step 3 to amount asked for If amount in grams: Multiply by formula weight If amount in particles: Multiply by 6.02E 23

5. Calculate theoretical yields from chemical equations. How many grams of hydrogen are produced from the decomposition of 1,234 g of water? Step 1: Write the balanced equation. Step 2: Convert grams to moles. Step 3:Ratio unknown to known. From Problem From Balanced Equation X moles of known x Coeff of Unknown = unknown Coeff of Known Step 4:Convert moles to grams. How many grams of hydrogen are produced from the decomposition of 1,234 g of water? 2H 2 O  2H 2 + O 2 1,234 g / 18.0 g/mol = 68.56 mol H 2 O From Problem From Equation: 68.56 Moles H 2 O x 2 H 2 = 68.56 Moles H 2 2 H 2 O Mass H 2 = 68.56 mol H 2 (2.02 g/ 1 mol) = 138 g (3 s.f.)

6. Calculate theoretical yields from chemical equations. How many grams of sodium carbonate are needed to precipitate the calcium from 254 g of calcium chloride? Step 1: Write the balanced equation. Step 2: Convert grams to moles. Step 3:Ratio unknown to known. From Problem From Balanced Equation X moles of known x Coeff of Unknown =unknown Coeff of Known Step 4:Convert moles to grams. How many grams of sodium carbonate are needed to precipitate the calcium from 254 g of calcium chloride? CaCl 2 + Na 2 CO 3  CaCO 3 + 2NaCl 254 g x 1 mol = 2.29 mol CaCl 2 – 111.1 g From Problem From Equation: 2.29 Moles CaCl 2 x 1 Na 2 CO 3 = X 1 CaCl 2 X = 2.29 moles Na 2 CO 3 Mass Na 2 CO 3 = 2.29 mol Na 2 CO 3 (106.0 g/ 1 mol) = 243 g (3 s.f.)

7. Calculate theoretical yields from chemical equations. How much oxygen does it take to burn 100.0 grams of octane Step 1: 2C 8 H 18 + 25O 2  16CO 2 + 18H 2 O

8. Calculate theoretical yields from chemical equations. How much oxygen does it take to burn 100.0 grams of octane Step 1: 2C 8 H 18 + 25O 2  16CO 2 + 18H 2 O Step 2:The moles of octane = 100.0 g x 1 mol = 0.8772 mol 114.0 g

9. Calculate theoretical yields from chemical equations. How much oxygen does it take to burn 100.0 grams of octane Step 1:2C 8 H 18 + 25O 2  16CO 2 + 18H 2 O Step 2:The moles of octane = 100.0 g x 1 mol = 0.8772 mol 114.0 g Step 3:Moles of O 2 required: 0.8772 C 8 H 18 x 25 O 2 = 10.97 mol O 2 2 C 8 H 18

10. Calculate theoretical yields from chemical equations. How much oxygen does it take to burn 100.0 grams of octane Step 1:2C 8 H 18 + 25O 2  16CO 2 + 18H 2 O Step 2:The moles of octane = 100.0 g x 1 mol = 0.8772 mol 114.0 g Step 3:Moles of O 2 required: 0.8772 C 8 H 18 x 25 O 2 = 10.97 mol O 2 2 C 8 H 18 Step 4:Mass of O 2 required: 10.97 mol (32.0 g/ 1 mol) = 351 g O 2

11. Calculate theoretical yields from chemical equations. In a spectacular reaction called the thermite reaction, iron(III) oxide reacts with aluminum producing iron and aluminum oxide. How many grams of iron will be produced from 43.7 grams of aluminum?

12. Calculate theoretical yields from chemical equations. In a spectacular reaction called the thermite reaction, iron(III) oxide reacts with aluminum producing iron and aluminum oxide. How many grams of iron will be produced from 43.7 grams of aluminum? Step 1:Fe 2 O 3 + 2Al  2Fe + Al 2 O 3 Step 2:The moles of Al = 43.7 g x 1 mol = 1.62 mol 27.0 g Step 3:Moles of Fe reproduced: 1.62 Al x 2 Fe = 1.62 mol Fe 2 Al Step 4:Mass of Fe produced: 1.62 mol (55.80 g/ 1 mol) = 90.4 g Fe