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Stoichiometry

Stoichiometry. TOPICS. Everyday Stoichiometry Simple Stoichiometry Calculating Amount of Product or Reactant Limiting Reagent Percent Yield. Standards Addressed:. Conservation of Matter and Stoichiometry

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Stoichiometry

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  1. Stoichiometry

  2. TOPICS • Everyday Stoichiometry • Simple Stoichiometry • Calculating Amount of Product or Reactant • Limiting Reagent • Percent Yield

  3. Standards Addressed: Conservation of Matter and Stoichiometry • 3a. Students know how to describe chemical reactions by writing balanced chemical equations • 3d. Students know how to determine the molar mass of a molecule from its chemical formula and a table of atomic masses an how to convert the mass of a molecular substance to moles, number of particles, or volume of gas at STP. • 3e. Students know how to calculate the masses of reactants and products in a chemical reaction from the mass of one of the reactants or products and the relevant atomic masses.

  4. Definitions • Stoichiometry: the study of mass relationships on chemical equations. • Excess: more than enough available; won’t run out of that reactant • Mole-mole ratio: how two substances are numerically related to each other in units of moles; you get these numbers from the balanced chemical equation.

  5. Everyday Stoichiometry: • 2 wheels + 1 frame → 1 bike • How many wheels and frames do you need to make 5 bikes? • If you have 6 wheels and 4 frames, how many bikes can you make? • If you have 11 wheels and 3 frames, how many bikes can you make?

  6. TOPICS • Everyday Stoichiometry • Simple Stoichiometry • Calculating Amount of Product or Reactant • Limiting Reagent • Percent Yield

  7. Simple Stoichiometry: • Here is the “recipe” for water: • 2 H2 + O2 → 2 H2O • *This recipe says: • 2 molecules of H2 react with 1 molecule of O2 to produce 2 molecules of water • 2 moles of H2 react with 1 mole of O2 to produce 2 moles of water

  8. Question • How many hydrogens and oxygens do you need to make 8 waters? • How many waters can you make from: • 10 H2 and 4 O2 • 5 H2 and 3 O2 • 25 H2 and 16 O2 • Which of each is in excess?

  9. Question • Here is the “recipe” for diphosphorus pentoxide: • 4 P + 5 O2→2 P2O5 • How many phosphorus and oxygens do you need to make 4 diphosphorus pentoxide? • How many diphosphorus pentoxide can you make from: • 12 P and 20 O2 • 21 P and 21 O2

  10. TOPICS • Everyday Stoichiometry • Simple Stoichiometry • Calculating Amount of Product or Reactant • Limiting Reagent • Percent Yield

  11. Mole-Mole Ratios • Come from the balanced chemical equation • Ratio made between the “given” substance and the “get” substance • Use the coefficients of the “given” and “get” from the balanced chemical equation • Ratios can be between any 2 substances • Reactant-reactant • Reactant-product • Product-product

  12. Mole-Mole Ratio Examples • 2 H2 + O2 → 2 H2O • 2 mole H22 mole H2O 1 mole O2 2 mole H2

  13. Mole-Mole Ratio Examples Fe2O3 (s) + 3 CO (g)→ 2 Fe (s) + 3 CO2 (g) • Write a mol-mol ratio between the reactants… • Write a mol-mol ratio between a product and a reactant… • Write a mol-mol ratio between a product and a product

  14. Calculating Amount of Reactant Needed • 2 P + 3Cl2 → 2 PCl3 • How many moles of phosphorus are consumed if 12 moles of phosphorus trichloride are produced?

  15. How Much Product is Produced? • 2 P + 3Cl2 → 2 PCl3 • How many moles of PCl3 can be formed from 5 moles chlorine and excess phosphorus?

  16. Question • 2 H2 + O2 → 2 H2O • How many moles of water are produced by burning 2.72 mol H2 in an excess of O2?

  17. Question • 2 H2 + O2 → 2 H2O • What mass of O2 is consumed in the complete combustion of 6.86g H2 ?

  18. Question • 2 Ag2CO3 (s) → 4 Ag(s) + 2CO2(g) + O2(g) • How many grams of Ag2CO3 must have decomposed if 75.1 grams of Ag were obtained in the reaction?

  19. Question • 2 Ag2CO3 (s) → 4 Ag(s) + 2CO2(g) + O2(g) • How many grams of carbon dioxide were produced if 25.0 g of oxygen were produced?

  20. Let’s Summarize the Steps • Is there a balanced chemical equation? • Write down the “given” and the “get” • Mini road map…g-mol-mol-g • Set-up a dimensional analysis equation • Cancel units and calculate • Report answer to correct # of sig. figs.

  21. THE LONGEST “MINI ROAD MAP” YOU WILL HAVE TO FOLLOW • GRAMS-MOLES-MOLES-GRAMS

  22. Question • KClO3 + 5 KCl + 6 HNO3 → 6KNO3 + 3Cl2 + 3 H2O • How many grams of KClO3 are required to prepare 10.0g of Cl2 ?

  23. Iron (II) oxide decomposes into iron and oxygen gas. • 2 FeO → 2 Fe + O2 • How many grams of FeO are needed to produce 140g of Fe?

  24. Hydrochloric acid reacts with zinc metal to produce zinc chloride and hydrogen gas • 2 HCl + 2 Zn → ZnCl2 + H2 • How many grams of hydrochloric acid are required to react completely with 1.00g of zinc?

  25. Topics • Everyday Stoichiometry • Simple Stoichiometry • Calculating Amount of Product or Reactant • Limiting Reagent • Percent Yield

  26. Anticipatory Set • 3 cups flour + 2 cups sugar + 1 cup butter + 3 eggs = 1 batch • Flour Sugar Butter Eggs 13 cups 10 cups 3 cups 20 • How many batches of cookies can we make? How did you figure it out? • Flour-4 Sugar-5 Butter-3 Eggs-7, so we can only make 3 batches. The butter yields the smallest amount possible that can be produced. The butter tells how many bathes we can make; therefore the butter is the limiting ingredient.

  27. Summarize • Here, we did multiple calculations side by side and then chose the correct result. • We can use this same type of reasoning/procedure to calculate the limiting reagent in a given chemical reaction.

  28. Definition • Limiting reagent: the reactant that is completely used up in the chemical reaction. The limiting reagent determines how much product can be formed. Calculating Limiting Reactant • Which reactant will run out first? You can’t tell just by looking at it, so you need to do some calculations. • NOTE: In limiting reagent problems, BOTH REACTANTS are converted to the same PRODUCT

  29. Calculating the Limiting Reagent • P4 + 6 Cl2 → 4 PCl3 What mass of PCl3 forms in the rxn of 125g P4 with 323 g Cl2?

  30. Limiting Reagent • CH4 + 2 O2 → CO2 + 2 H2O • If 12.0g CH4 and 30.0g O2 react to form CO2 and H2O, how many grams of CO2 will be formed?

  31. Summarize the Steps we followed 1. Is there a balanced chemical equation? 2. Write down the 2 “givens” (both reactants) and the “get” (the product) 3. Set-up Dimensional Analysis equations; 1 for each given • g-mol-mol-g 4. Whichever reactant produced the smaller amount of product, that reactant is the limiting reagent 5. Make your concluding statement

  32. Topics • Everyday Stoichiometry • Simple Stoichiometry • Calculating Amount of Product or Reactant • Limiting Reagent • Percent Yield

  33. Definitions • Theoretical Yield: How much product you expect to get based on your calculation • Actual Yield: Amount of product actually produced when the reaction is conducted… this amount is always stated in the problem • Percent Yield: the percentage of theoretical yield obtained from the reaction

  34. Calculating Percent Yield • % Yield = actual yield X 100% theoretical yield

  35. Calculating Percent Yield Determine the percent yield for the reaction between 98.7g of Sb2S3 and excess oxygen if 72.4 g of Sb4O6 are recovered along with an unknown amount of sulfur dioxide gas.

  36. Determine the percent yield for the reaction between 46.5 g of ZnS and excess oxygen if 18.4 g of ZnO are recovered along with an unknown amount of sulfur dioxide gas. Percent Yield

  37. END

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