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Chapter 12

Stoichiometry Roadmap. Chapter 12. Stoichiometry. Composition Stoichiometry – mass relationships of elements in compounds Reaction Stoichiometry – mass relationships between reactants and products in a chemical reaction. Visual Concepts. Stoichiometry.

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Chapter 12

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  1. Stoichiometry Roadmap Chapter 12 Stoichiometry

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

  3. Visual Concepts Stoichiometry Click below to watch the Visual Concept. Visual Concept

  4. Mole Ratio – conversion factor (unit factor) that relates one chemical to another – comes from the coefficients in a chemical equation 2 Al2O3 4 Al + 3 O2 2 mol Al2O3 yields 4 mol Al 2 mol Al2O3 yields 3 mol O2

  5. Section1 Introduction to Stoichiometry 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:2 mol Al2O3 2 mol Al2O3 4 mol Al 4 mol Al 3 mol O2 3 mol O2 , ,

  6. 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.

  7. Visual Concepts Molar Mass as a Conversion Factor Click below to watch the Visual Concept. Visual Concept

  8. Visual Concepts Conversion of Quantities in Moles Click below to watch the Visual Concept. Visual Concept

  9. Section2 Ideal Stoichiometric Calculations Solving Stoichiometry Problems with Moles or Grams

  10. How many grams of ammonia can you make with 25 grams of hydrogen? N2 + 3H2 2NH3 You are given the mass of 25 grams of hydrogen. Start there. 141.67 g NH3

  11. Visual Concepts Mass and Number of Moles of an Unknown Click below to watch the Visual Concept. Visual Concept

  12. What mass of oxygen will react with 96.1 grams of propane? First, write the balanced reaction: C3H8(g) + 5 O2(g) → 3 CO2(g) + 4 H2O(g) Second, convert the mass to moles. Note that the molecular weight of propane is 44.1 g/mole.

  13. Section3 Limiting Reactants and Percentage Yield 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.

  14. Visual Concepts Limiting Reactants and Excess Reactants Click below to watch the Visual Concept. Visual Concept

  15. 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 NH3(g) + 3 CuO(s) → N2(g) + 3 Cu(s) + 3 H2O(g) If 18.1 g of NH3 are reacted with 90.4 g of CuO, which is the limiting reagent? How many grams of N2 will be formed?

  16. Section3 Limiting Reactants and Percentage Yield 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.

  17. Visual Concepts Comparing Actual and Theoretical Yield Click below to watch the Visual Concept. Visual Concept

  18. What is the % yield of N2 in the previous problem if only 0.95 g were actually obtained from the reaction?

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