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Stoichiometry – Ch 9 Limiting/Excess Reactants and Percent Yield.

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Presentation on theme: "Stoichiometry – Ch 9 Limiting/Excess Reactants and Percent Yield."— Presentation transcript:

1 Stoichiometry – Ch 9 Limiting/Excess Reactants and Percent Yield

2 Limiting Reactants Available Ingredients – 4 slices of bread – 1 jar of peanut butter – ½ jar of jelly Limiting Reactant: bread Excess Reactants: peanut butter and jelly

3 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 and easier to recycle

4 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

5 Limiting Reactants 79.1 g of zinc react with 2.25 moles of HCl. Indentify the limiting and excess reactants. How many liters of hydrogen are formed at STP? Zn + 2HCl  ZnCl 2 + H g2.25 mole? L

6 Limiting Reactants Zn + 2HCl  ZnCl 2 + H g2.25 mole? L 79.1 g Zn x 1mol Zn x 1 mol H 2 x 22.4 L H g Zn 1 mol Zn1 mol H 2 = 27.3 L H 2

7 Limiting Reactants Zn + 2HCl  ZnCl 2 + H g2.25 mole? L 2.25 mol HCl x 1 mol H 2 x 22.4 L H mol HCl 1 mol H 2 = L H 2

8 Limiting Reactants Starting with Zn – 27.3 L H 2 Starting with HCl – 25.2 L H 2 Limiting Reactant: HCl Excess Reactant: Zn Product Formed: 25.2 L H 2

9 Percent Yield % yield = actual yield (measure in lab) x 100 theoretical yield (calculate)

10 Percent Yield When 45.8 g of K 2 CO 3 react with excess HCl, 46.3 g of KCl are formed. Calculate the theoretical and percent yields of KCl. K 2 CO 3 + 2HCl  2KCl + H 2 O + CO g ? g 46.3 g (actual yield)

11 Percent Yield K 2 CO 3 + 2HCl  2KCl + H 2 O + CO g ? g (theoretical yield) 46.3 g (actual yield) Theoretical yield: 45.8 g K 2 CO 3 x 1mol K 2 CO 3 x 2 mol KCl x 74.5 g KCl g K 2 CO 3 1 mol K 2 CO 3 1 mol KCl = g KCl

12 Percent Yield K 2 CO 3 + 2HCl  2KCl + H 2 O + CO g49.5 g (theoretical yield) 46.3 g (actual yield) % yield = 46.3 x 100 = 93.5% 49.5


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