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Stoichiometry

Stoichiometry. Chapter 9. Big picture. Ch . 7 The mole Ch.8 Balancing Chemical Equations Ch.9 “Stoichiometry ” Target : How many grams of carbon dioxide are produced by burning 411 g of gasoline?. Notes. Stoichiometry

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Stoichiometry

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  1. Stoichiometry Chapter 9

  2. Big picture • Ch. 7 The mole • Ch.8 Balancing Chemical Equations • Ch.9 “Stoichiometry” Target: How many grams of carbon dioxide are produced by burning 411 g of gasoline?

  3. Notes Stoichiometry Theproportionalrelationshipbetweentwoormoresubstancesduringachemicalreaction. The proportional relationship between two or more substances during a chemical reaction.

  4. Real world stoichiometry problem 1 stick of butter + 3 eggs  2 cupcakes 1. If you have 60 eggs how many cupcakes can you make? (assuming you have unlimited butter) 2. How many eggs does it take to make 300 cupcakes? 1. ANS = 40 cupcakes 2. ANS = 450 eggs

  5. 9.1 Practice: mole-to-mole conversion C3H8+ 5O2 3CO2 + 4H2O You have 4 mole of propane, (C3H8) • How many moles of O2will it react with when it burns? • How many moles of CO2form when it burns? • How many moles of H2O form when it burns?

  6. 9.1 Practice: Mole-to-mole conversion Given the following equation: N2 + 3H2 2NH3 Calculate the number of moles of hydrogen needed to prepare 312 moles of ammonia. See Graphic Organizer on p. 303

  7. Notes Mole Ratio Used as conversion factor in stoichiometry problems. x moles of unknown y moles of given x = coefficient of unknown in balanced chem eqn y = coefficient of given in balanced chem eqn

  8. 9.1 Mole to Mole conversions Practice P. 304 # 1a,b # 2 a,b,c P. 329 #21*,22,23 *h’wk

  9. Mass-to-Mass conversion See step-by-step procedure on p. 305 See graphic organizer on p. 306

  10. Mass-to-Mass conversion Typical Question Imagine 7.5g of nitrogen gas (N2) reacts with excess* hydrogen gas per the following equation: N2 + 3H2 2NH3 Calculate the mass of ammonia (NH3)produced * Excess= “An amount or quantity beyond what is sufficient; a surplus.” = IGNORE!

  11. Mass-to-Mass conversion Imagine 7.5g of nitrogen gas (N2) reacts with excess hydrogen gas per the following equation: N2 + 3H2 2NH3 Calculate the mass of ammonia (NH3)produced. • What is the ‘Given’ in the question? • What is the ‘Unknown’ in the question? • What is the molar mass of given and unknown? • What is the mole ratio that connects the Given and the Unknown? ANSWER = 9.1 g

  12. Stoichiometry calcs SUMMARY WHEN IN DOUBT……TO BEGIN, CONVERT GIVEN TO MOLES When one of the reactants is in excess  ignore it.

  13. 9.1 Stoichiometry problems involving mass What mass of NH3 can be made from 1221g of H2? N2 + 3H22NH3 See Skills Toolkit 3 p. 306

  14. 9.1 Stoichiometry Problems Involving Mass Sample Problem B (Follow along on P. 307) What mass of NH3 can be made from 1221 g H2? N2 + 3H2 2NH3

  15. 9.1 Stoichiometry Problems Involving Mass What mass of NH3 can be made from 1221g of H2? N2 + 3H22NH3 GIVEN: • mass of H2 = 1221 g • molar mass of H2 = 2.02 g/mol • Mole ratio: 3 mol H2 = 2 mol NH3 UNKNOWN • mass of NH3 = ? g ( will need molar mass of NH3 = 17.04 g/mol)

  16. 9.1 Stoichiometry Problems Involving Mass Step 1: To change grams to moles, use the molar mass of H2. Step 2: The mole ratio must cancel out the units of mol H2 given in the problem and leave the units of mol NH3. • Therefore, the mole ratio is: Step 3: To change moles of NH3 to grams, use the molar mass of NH3.

  17. 9.1 Stoichiometry Problems Involving Mass

  18. 9.1 Problems Involving Mass For Mass Calculations, Use Molar Mass • A mass-mass problem is a three-step process. • Step 1: Convert the given mass into moles. • Step 2: Use the mole ratio to convert moles of given to moles of unknown. • Step 3: Convert moles of known into grams. • See page 305 for procedure

  19. Practice Calculate the mass of hydrogen that would be needed to make 100 g of ammonia.

  20. Practice: StoichiometryScratch paper Calculate the mass of water formed from the combustion of 83 g of ethane C2H6 Balance the equation GUESS Write the 3 conversion factors will you need ANS = 149 g

  21. 9.1 Practice p. 311 # 4 a,b How many grams of BrCl form when 212 g of Br2 react w/ excess Cl2?

  22. 9.1 Stoichiometry Problems Involving Mass Practice See page 305 for procedure P. 307 #1,2,3,4* P. 330 # 24,25*,26** * Show work to teacher when done ** Beast Mode

  23. Next Generation Science Standard (NGSS) HS-PS1-7. Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction. The Mole (Ch.7) Balancing Equations (Ch.8) Stoichiometry (Ch.9)

  24. ‘High Energy’ = ‘Reactive’ = ‘Unstable’ e.g. gasoline Low Energy = ‘Unreactive’ ‘Stable’ e.g. carbon dioxide Combustion:CH4 + 2O2CO2 + 2H2O

  25. Photosynthesis

  26. Global Warming

  27. 9.1 Stoichiometry Problems Involving Mass One gallon of gasoline (C8H18) weighs 2835 g. Calculate the mass of carbon dioxide produced by the combustion of one gallon of gasoline. Follow along w/ Skills Toolkit p. 306

  28. 9.1 Stoichiometry Problems Involving Mass Gathering Information • Write the balanced chemical equation for the combustion of octane, C8H18 • Calculate the molar mass of octane C8H18 • Calculate the molar mass of carbon dioxide

  29. Mass-Mass Stoich:Cellular Respiration Calculate the number of grams of water that would theoretically be produced in cellular respiration by the combustion of 75.2 g of glucose.

  30. Brainteaser A bike shop has 10 bike frames and 16 wheels. How many complete bicycles can be assembled using these parts? What would be left over? 8 complete bicycles. 2 frames left over.

  31. Notes Limiting Reactant Thesubstancethatcontrolsthequantityofproductthatcanforminachemicalreaction

  32. Notes Limiting Reactant The substance that controls the quantity of product that can form in a chemical reaction. It runs out first  Excess Reactant Thesubstancethatisnotusedupcompletelyinachemicalreaction

  33. Notes Excess Reactant The substance that is not used up completely in a chemical reaction. Ignore it! P. 313

  34. Real world analogy: Limiting reagent 1egg + 3 spoonfuls of butter  2 cupcakes If you have 9 eggs and 9 spoonfuls of butter, how many cupcakes can you make? What ingredients would be left over? How much? What ingredient would run out first? 6 cupcakes (theoretical yield) 6 eggs left over (eggs are in excess) Butter is the ‘limiting reactant’.

  35. 9.2 Limiting Reagent and Theoretical Yield Practice: p. 331 # 33 p. 317 # 1,3,2

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