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Chemistry 103

Chemistry 103. Lecture 15. Outline. I. Chemical Reactions - balancing (review) II. Stoichiometry - Limiting Reactant III. Classification of Reaction Types. Molar Mass from Periodic Table. Molar mass Is the atomic mass expressed in grams. Avogadro’s Number.

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Chemistry 103

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  1. Chemistry 103 Lecture 15

  2. Outline I. Chemical Reactions - balancing (review) II. Stoichiometry - Limiting Reactant III. Classification of Reaction Types

  3. Molar Mass from Periodic Table Molar mass • Is the atomic mass expressed in grams

  4. Avogadro’s Number • Solution = 6.022 x 1023 • Avogadro’s number is equal to 1 mole • Makes working with large numbers easier

  5. The Mole Molar mass 1 mole 6.022 x 1023 Mass in grams Individual particles

  6. Concept Review • Do 7.0g of CO and 7.5 g of C2H6 contain the same number of C atoms? (Prove your answer mathematically) A. YES B. NO

  7. Chemical Reaction In a chemical reaction, • Old bonds are broken and new bonds are formed • Atoms in the reactants are rearranged to form one or more different substances • Fe and O2 form rust (Fe2O3)

  8. Chemical’s Shorthand - Chemical Rxn • Fe (s) + O2(g) --------> Fe2O3 (s) • 2Fe(s) + O2(g) --------> Fe2O3(s) • 4Fe(s) + O2(g) --------> 2Fe2O3(s) • 4Fe(s) + 3O2(g) --------> 2Fe2O3(s) • BALANCED!!!!!

  9. Balancing Practice • Li3N(s) -------> Li(s) + N2(g) • Mg + H3PO4 ------> Mg3(PO4)2 + H2 • MgCl2 + AgNO3 ------> Mg(NO3)2 + AgCl

  10. Stoichiometry • Chemical Stoichiometry: using mass and quantity relationships among reactants and products in a chemical reaction to make predictions about how much product will be made.

  11. Moles in Equations • We can read the equation in “moles” by placing the word “mole” or “mol” between each coefficient and formula. 4Fe(s) + 3O2(g) 2Fe2O3(s) 4 mol Fe + 3 mol O22 mol Fe2O3

  12. Mole to Mole problems • Using the balanced chemical reaction, how many moles of O2 will react with 4.28 moles of CS2 to produce CO2 and SO2? CS2 + O2 ------> CO2 + SO2 (unbalanced)

  13. Mole to Mole problems • When 4.28 moles of CS2 reacts according to the balanced chemical equation below, how many moles of CO2 will be produced? CS2 + 3O2 ------> CO2 + 2SO2

  14. Mole to Mole problems • When 4.28 moles of CS2 reacts according to the balanced chemical equation below, how many moles of SO2 will be produced? CS2 + 3O2 ------> CO2 + 2SO2

  15. Reaction Interpretation • Using the balanced chemical reaction, how many moles of O2 will react with 4.28 moles of CS2 to produce CO2 and SO2? CS2 + 3O2 ------> CO2 + 2SO2 BEFORE AFTER

  16. Moles-to-Grams or Grams-to-Mole

  17. Chemical Stoichiometry 2H2 + O2 ----> 2H2O mole to mole comparisons: How many moles of O2 are needed to produce 1.39 moles of H2O?

  18. Chemical Stoichiometry 2H2 + O2 ----> 2H2O mole to gram or gram to mole comparisons: How many moles of O2 are needed to produce 7.4g of H2O?

  19. Chemical Stoichiometry 2H2 + O2 ----> 2H2O mole to mole comparisons: How many moles of O2 are needed to exactly react with 4.28 moles of H2?

  20. Chemical Stoichiometry 2H2 + O2 ----> 2H2O mole to gram or gram to mole comparisons: How many moles of O2 are needed to exactly react with 12.4g of H2?

  21. Grams-to-Mole How many grams of O2 are needed to produce 0.400 mol Fe2O3? 4Fe(s) + 3O2(g) 2 Fe2O3(s) A) 38.4 g O2 B) 19.2 g O2 C) 1.90 g O2

  22. “gram to gram” calculations

  23. Calculating the Mass of a Reactant The reaction between H2 and O2 produces 13.1 g water. How many grams of O2 reacted? 2H2(g) + O2(g) 2H2O(g) Plan: g H2O mole H2O mole O2 g O2

  24. Calculating the Mass of a Reactant The reaction between H2 and O2 produces 13.1 g water. How many grams of O2 reacted? 2H2(g) + O2(g) 2H2O(g) Before: x g After: 13.1 g Plan: g H2O mole H2O mole O2 g O2

  25. Mass calculations • How many grams of CS2 are needed to completely react with 6.0g of O2 according to the following reaction? • CS2 + 3O2 ------> CO2 + 2SO2

  26. “gram to gram” continued…. • One way to remove gaseous carbon dioxide from the air in a spacecraft is to let canisters of solid lithium hydroxide absorb it according to the following reaction: 2LiOH(s) + CO2(g) ------> Li2CO3(s) + H2O(l) How many grams of LiOH must be used to produce 10.0g of Li2CO3?

  27. Learning Check Acetylene gas C2H2 burns in the oxyacetylene torch for welding. How many grams of C2H2 are burned if the reaction produces 75.0 g CO2? 2C2H2(g) + 5O2(g) 4CO2(g) + 2H2O(g) A) 88.6 g C2H2 B) 44.3 g C2H2 C) 22.2 g C2H2

  28. Chemical Reactions Limiting Reactant & Percent Yield

  29. Limiting Reactant A limiting reactant in a chemical reaction is the substance that: • Is used up first • Stops the reaction • Limits the amount of product that can form

  30. Reacting Amounts In a table setting, there is 1 plate, 1 fork, 1 knife, and 1 spoon. How many table settings are possible from 5 plates, 6 forks, 4 spoons, and 7 knives? What is the limiting item?

  31. Reaction Equivalent • 1plate + 1fork + 1knife + 1spoon ----> 1place setting • BEFORE 5 6 7 4 0 • AFTER 1 2 3 0 4 LR

  32. Reacting Amounts In a table setting, there is 1plate, 2 forks, 1 knife, and 1spoon. How many table settings are possible from 5 plates, 6 forks, 4 spoons, and 7 knives? What is the limiting item?

  33. Reaction Equivalent • 1plate + 2fork + 1knife + 1spoon ----> 1place setting • BEFORE 5 6 7 4 0 • AFTER 2 0 4 1 3 LR

  34. Limiting Reactants When 4.00 mol H2 is mixed with 2.00 mol Cl2,how many moles of HCl can form? H2(g) + Cl2(g)  2HCl (g) 4.00 mol 2.00 mol ??? Mol STEPS: • Calculate the moles of product from each reactant, H2 and Cl2. • The limiting reactant is the one that produces the smallest amount of product.

  35. Checking Calculations

  36. Limiting Reactant If 4.80 grams Ca mixed with 2.00 grams N2, which is the limiting reactant? 3Ca(s) + N2(g)  Ca3N2(s)

  37. Limiting Reactants Using Mass Calculate the mass of water produced when 8.00 g H2 and 24.0 g O2 react? 2H2(g) + O2(g) 2H2O(l)

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