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Chapter 9

Chapter 9. Stoichiometry. Stoichiometry. Composition stoichiometry Mass relationships of elements in compounds Reaction stoichiometry Mass relationships between reactants and products. Reaction Stoichiometry. Use ratios from balanced equation Problem Type 1

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Chapter 9

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  1. Chapter 9 Stoichiometry

  2. Stoichiometry • Composition stoichiometry • Mass relationships of elements in compounds • Reaction stoichiometry • Mass relationships between reactants and products

  3. Reaction Stoichiometry • Use ratios from balanced equation • Problem Type 1 • Given & unknown quantities in moles • Problem Type 2 • Given in moles & unknown in grams

  4. Reaction Stoichiometry • Problem Type 3 • Given in grams & unknown in moles • Problem Type 4 • Given in grams & unknown in grams

  5. Mole Ratio • Conversion factor that relates amount of moles of substances 2Al2O3(l)  4Al(s) + 3O2(g) • How many moles of aluminum can be produced from 13.0 mol of aluminum oxide?

  6. Molar Mass • The mass (in g) of 1 mole of substance 2Al2O3(l)  4Al(s) + 3O2(g) • How many grams of Al is equivalent to 26.0 mol Al?

  7. Conversions • Problem Type 1 • Mole to mole • One conversion factor: mole ratio • Given (mol) x mole ratio (mol/mol) = unknown (mol)

  8. Conversions • In a spacecraft, the CO2 exhaled by astronauts can be removed by its reaction with lithium hydroxide, LiOH, according to the following chemical equation. CO2(g) + 2LiOH(s)  Li2CO3(s) + H2O(l) • How many moles of LiOH are required to react with 20 mol of CO2, the average amount exhaled by a person each day?

  9. Conversions • The disinfectant hydrogen peroxide, H2O2, decomposes to form water and oxygen gas. How many moles of O2, will result from the decomposition of 5 mol of hydrogen peroxide?

  10. Conversions • Problem Type 2 • Mole to mass • Two conversion factors: mole ratio & molar mass • Given (mol) x mole ratio (mol/mol) x molar mass (g/mol) = unknown (g)

  11. Conversions • In photosynthesis, plants use energy from the sun to produce glucose C6H12O6, and oxygen from the reaction of CO2 and H2O. What mass, in grams, of glucose is produced when 3.00 mol of H2O with CO2?

  12. Conversions • What mass of CO2, in grams, is needed to react with 3.00 mol of H2O in the photosynthetic reaction described on the last slide?

  13. Conversions • Problem Type 3 • Mass to moles • Two conversion factors: molar mass & mole ratio • Given (g) x molar mass (mol/g) x mole ratio (mol/mol) = unknown (mol)

  14. Conversions • The first step in the industrial manufacture of nitric acid is the catalytic oxidation of ammonia, NH3(g) + O2(g)  NO(g) + H2O(g) (unbalanced) The reaction is run using 824 g of NH3 and excess oxygen. a.How many moles of NO are formed? b.How many moles of H2O are formed?

  15. Conversions • The compound PtCl2(NH3)2 is effective as a treatment for some cancers. It is synthesized by the reaction shown in the following equation: K2PtCl4 + 2NH3 2KCl + PtCl2(NH3)2 a.How many moles of K2PtCl4 must react in order to produce 30.0 g of PtCl2(NH3)2? b.How many moles of NH3 are needed to produce 30.0 g of PtCl2(NH3)2?

  16. Conversions • Problem Type 4 • Mass to mass • Three conversion factors: molar mass, mole ratio, molar mass • Given (g) x molar mass (mol/g) x mole ratio (mol/mol) x molar mass (g/mol) = unknown (g)

  17. Conversions • Tin(II) fluoride, SnF2, is used in some toothpastes. It is made by the reaction of tin with hydrogen fluoride according to the following equation. Sn + 2HF  SnF2 + H2 How many grams of SnF2 are produced from the reaction of 30.00 g of HF with Sn?

  18. Conversions • Sodium peroxide reacts vigorously with water to produce sodium hydroxide and oxygen. The unbalanced equation is the following: Na2O2 + H2O  NaOH + O2 • What mass in grams of O2 is produced when 50.0 g of Na2O2 react? b. What mass in grams of water is needed to react completely with the Na2O2?

  19. Limiting Reactants • One reactant is present in excess • When one reactant is used up reaction is over • Limiting reactant • Limits the production of product • Excess reactant • Not completely used up

  20. Limiting Reactants • C(s) + O2(g)  CO2(g) • 5 mol C • 10 mol O2 • More than enough O2 - 5 mol excess • Limiting - Carbon

  21. Problem • Silicon dioxide (quartz) is usually quite unreactive but reacts readily with hydrogen fluoride according to the following equation. SiO2 + 4HF  SiF4 + 2H2O If 2.0 mol of HF are exposed to 4.5 mol of SiO2, which is the limiting reactant?

  22. Problem • The black oxide of iron, Fe3O4, occurs in nature as the mineral magnetite. This substance can also be made in the laboratory by the reaction between red-hot iron and steam according to the following equation. 3Fe + 4H2O  Fe3O4 + 4H2

  23. Problem 3Fe + 4H2O  Fe3O4 + 4H2 a. When 36.0 g of H2O is mixed with 167 g of Fe, which is the limiting reactant? b. What mass in grams of black iron oxide is produced? c. What mass in grams of excess reactant remains when the reaction is completed?

  24. Percent Yield • Theoretical yield • Maximum amount of product • Actual yield • Measured amount of product produced • Efficiency express in percent yield % yield = (actual yield)/(theoretical yield) x 100

  25. Problem • Chlorobenzene, C6H5Cl, is used in the production of many important chemicals, such as aspirin, and disinfectants. One industrial method of preparing chlorobenzene is to react benzene, C6H6, with chlorine, which is represented by the following equation.

  26. C6H6 + Cl2 C6H5Cl + HCl • When 36.8 g of C6H6 react with an excess of Cl2, the actual yield of C6H5Cl is 38.8 g. What is the percent yield of C6H5Cl?

  27. Problem • Huge quantities of sulfur dioxide are produced from zinc sulfide by means of the following reaction. 2ZnS + 3O2 2ZnO + 2SO2 If the typical yield is 86.78%, how much SO2 should be expected if 4897 g of ZnS are used

  28. Chapter Review • Pg. 295 • 8, 10, 11, 12, 14, 15, 22, 23, 24, 26, 28, 33

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