1. Chapter 12 Stoichiometry

4. Composition Stoichiometry – mass relationships of elements in compounds Reaction Stoichiometry – mass relationships between reactants and products in a chemical reaction

5. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 9 Visual Concepts Click below to watch the Visual Concept. Stoichiometry Visual Concept

6. Mole Ratio – conversion factor (unit factor) that relates one chemical to another – comes from the coefficients in a chemical equation 2 Al 2 O 3  4 Al + 3 O 2 2 mol Al 2 O 3 yields 4 mol Al 2 mol Al 2 O 3 yields 3 mol O 2

7. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 9 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: 2Al 2 O 3 (l)  4Al(s) + 3O 2 (g) Mole Ratios: 2 mol Al 2 O 3 2 mol Al 2 O 3 4 mol Al 4 mol Al 3 mol O 2 3 mol O 2,, Section 1 Introduction to Stoichiometry

10. In the standard stoichiometry calculations you should know, ALL ROADS LEAD TO MOLS. You can change any amount of any measurement of any material in the same equation with any other material in any measurement in the same equation. That is powerful. The setup is similar to Dimensional Analysis. 1. Start with what you know (GIVEN), expressing it as a fraction. 2. Use definitions or other information to change what you know to mols of that material. 3. Use the mol ratio to exchange mols of the material given to the mols of material you want to find. 4. Change the mols of material you are finding to whatever other measurement you need.

11. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 9 Visual Concepts Click below to watch the Visual Concept. Visual Concept Molar Mass as a Conversion Factor

12. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 9 Visual Concepts Click below to watch the Visual Concept. Visual Concept Conversion of Quantities in Moles

13. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 9 Solving Stoichiometry Problems with Moles or Grams Section 2 Ideal Stoichiometric Calculations

14. How many grams of ammonia can you make with 25 grams of hydrogen? N 2 + 3H 2  2NH 3 You are given the mass of 25 grams of hydrogen. Start there. 141.67 g NH 3

15. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 9 Visual Concepts Click below to watch the Visual Concept. Visual Concept Mass and Number of Moles of an Unknown

16. What mass of oxygen will react with 96.1 grams of propane? First, write the balanced reaction: C 3 H 8(g) + 5 O 2(g) → 3 CO 2(g) + 4 H 2 O (g) Second, convert the mass to moles. Note that the molecular weight of propane is 44.1 g/mole.

17. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 9 Limiting Reactants The limiting reactant is the reactant that limits the amount of the other reactant that can combine and the amount of product that can form in a chemical reaction. The excess reactant is the substance that is not used up completely in a reaction. Section 3 Limiting Reactants and Percentage Yield

18. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 9 Visual Concepts Click below to watch the Visual Concept. Visual Concept Limiting Reactants and Excess Reactants

19. Limiting Reactant – reactant that controls the amount of product that can be produced For example, nitrogen gas is prepared by passing ammonia gas over solid copper(II) oxide at high temperatures. The other products are solid copper and water vapor. 2 NH 3 (g) + 3 CuO(s) → N 2 (g) + 3 Cu(s) + 3 H 2 O(g) If 18.1 g of NH 3 are reacted with 90.4 g of CuO, which is the limiting reagent? How many grams of N 2 will be formed?

20. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 9 Percentage Yield The theoretical yield is the maximum amount of product that can be produced from a given amount of reactant. The actual yield of a product is the measured amount of that product obtained from a reaction. The percentage yield is the ratio of the actual yield to the theoretical yield, multiplied by 100. Section 3 Limiting Reactants and Percentage Yield

21. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 9 Visual Concepts Click below to watch the Visual Concept. Visual Concept Comparing Actual and Theoretical Yield

22. What is the % yield of N 2 in the previous problem if only 0.95 g were actually obtained from the reaction?