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Stoichiometry. II. Stoichiometry in the Real World. A. Limiting Reactants. Available Ingredients 4 slices of bread 1 jar of peanut butter 1/2 jar of jelly. Limiting Reactant bread. Excess Reactants peanut butter and jelly. A. Limiting Reactants. Limiting Reactant used up in a reaction
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Stoichiometry II. Stoichiometry in the Real World
A. Limiting Reactants • Available Ingredients • 4 slices of bread • 1 jar of peanut butter • 1/2 jar of jelly • Limiting Reactant • bread • Excess Reactants • peanut butter and jelly
A. Limiting Reactants • Limiting Reactant • used up in a reaction • determines the amount of product • Excess Reactant • added to ensure that the other reactant is completely used up • cheaper & easier to recycle
A. Limiting Reactants 1. Write a balanced equation. 2. For each reactant, calculate the amount of product formed. 3. Smaller answer indicates: • limiting reactant • amount of product
A. Limiting Reactants • 79.1 g of zinc react with 81 g of 2.5M HCl. Identify the limiting and excess reactants. How many grams of hydrogen are formed? Zn + 2HCl ZnCl2 + H2 ? g 79.1 g 81g
A. Limiting Reactants Zn + 2HCl ZnCl2 + H2 ? g 79.1 g 81g 79.1 g Zn 1 mol Zn 65.39 g Zn 1 mol H2 1 mol Zn 2 g H2 1 mol H2 = 2.42g H2
A. Limiting Reactants Zn + 2HCl ZnCl2 + H2 ? g 79.1 g 81g 81g HCl 1 mol HCl 36 g HCl 1 mol H2 2 mol HCl 2 g H2 1 mol H2 = 2.25g H2
A. Limiting Reactants left over zinc Zn: 2.42g H2 HCl: 2.25g H2 Limiting reactant: HCl Excess reactant: Zn Product Formed:2.25g H2
B. Percent Yield measured in lab calculated on paper
B. Percent Yield • When 45.8 g of K2CO3 react with excess HCl, 46.3 g of KCl are formed. Calculate the theoretical and % yields of KCl. K2CO3 + 2HCl 2KCl + H2O + CO2 45.8 g ? g actual: 46.3 g
B. Percent Yield K2CO3 + 2HCl 2KCl + H2O + CO2 Theoretical Yield: 45.8 g ? g actual: 46.3 g 45.8 g K2CO3 1 mol K2CO3 138.21 g K2CO3 2 mol KCl 1 mol K2CO3 74.55 g KCl 1 mol KCl = 49.4 g KCl
B. Percent Yield 46.3 g 49.4 g K2CO3 + 2HCl 2KCl + H2O + CO2 Theoretical Yield = 49.4 g KCl 45.8 g 49.4 g actual: 46.3 g 100 = 93.7% % Yield =