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Stoichiometry and the Mole

Stoichiometry and the Mole. Chapter 9 . 9.1 Stoichiometry—What Is It?. Stoichiometry Study of quantitative aspects of chemistry Applies to balanced equations only Answers “How much?” Number of reactants needed Number of products produced. 9.1 Stoichiometry—What Is It? (Continued).

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Stoichiometry and the Mole

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  1. Stoichiometry and the Mole Chapter 9

  2. 9.1 Stoichiometry—What Is It? • Stoichiometry • Study of quantitative aspects of chemistry • Applies to balanced equations only • Answers “How much?” • Number of reactants needed • Number of products produced

  3. 9.1 Stoichiometry—What Is It? (Continued) Consider a cheesecake that requires five eggs to prepare. How many eggs would be needed to create two cheesecakes?

  4. 9.1 Stoichiometry—What Is It? (Continued) Consider a cheesecake that requires five eggs to prepare. How many eggs would be needed to create two cheesecakes? Since one cake requires five eggs, two cakes would require ten eggs.

  5. 9.1 Stoichiometry—What Is It? (Continued) • Unit analysis • Find the conversion between units. • 5 eggs = 1 cake • Use the conversion factor to find your answer.

  6. 9.1 Stoichiometry—What Is It? (Continued) If one cheesecake requires one cup of sugar and you have three cups of sugar, how many cheesecakes can be made?

  7. 9.1 Stoichiometry—What Is It? (Continued) If one cheesecake requires one cup of sugar and you have three cups of sugar, how many cheesecakes can be made? If each cake requires one cup of sugar and you have three cups, you can make a total of three cheesecakes.

  8. 9.2 The Mole • The mole • Relates number of atoms/molecules to grams • Cannot count individual atoms due to extreme small size • Is a set number of atoms/molecules • Similar to 12 items in a dozen

  9. 9.2 The Mole (Continued) • Consider the chemical equation : H2 + I2 2HI • This equation does not relate grams of compounds but instead number of molecules for each compound “One molecule of H2 reacts with one molecule of I2 to form 2 molecules of HI.”

  10. 9.2 The Mole (Continued) • Avogadro’s number • Number of atoms/molecules in one mole • 6.0223 x 1023 items • Can be a mole of atoms/molecules/doughnuts • Conversion factors 1 mole = 6.02 x 1023 items

  11. 9.2 The Mole (Continued) • What is a mole’s size? • Every grain of sand on Earth is roughly one mole. • One mole of water is roughly one swallow. • One mole of sugar would fill your cupped hands.

  12. 9.2 The Mole (Continued) • Since a mole is simply a number of items, both are correct.

  13. 9.2 The Mole (Continued) • So you can say: • 1 H2 molecule reacts with 1 I2 molecule to give 2 HI molecules, or • 1 dozen H2 molecules react with 1 dozen I2 molecules to give 2 dozen HI molecules or • 1 mole of H2molecules reacts with 1 mole of I2 molecules to give 2 moles of HI molecules.

  14. 9.2 The Mole (Continued) • Mole’s relationship with grams • We cannot count out individual atoms, so we mass out the amount of atoms.

  15. 9.2 The Mole (Continued) • Masses • Mole is defined as the number of carbon atoms in 12 g of . • So massing out 12 grams gives exactly 1 mole.

  16. 9.2 The Mole (Continued) • Mass of one C-12 atom: • And because 1 amu is 1/12th the mass of a atom, we can say: • Giving the mass of one carbon atom

  17. 9.2 The Mole (Continued) • Molar mass • Allows conversion between mass and moles and also moles to mass. • Simply replace atomic mass amu with grams to find the mass of one mole.

  18. 9.2 The Mole (Continued) Suppose you obtain 393.934 g of gold. (a) What is the molar mass of gold? (b) How many moles of gold do you have? (c) How many atoms of gold do you have?

  19. 9.2 The Mole (Continued) Suppose you obtain 393.934 g of gold. (a) What is the molar mass of gold? 196.967 grams per mole (b) How many moles of gold do you have? 2 moles of Au (c) How many atoms of gold do you have? 1.2045 x 1023 atoms of Au

  20. 9.2 The Mole (Continued) • Molar mass of molecules • Add each piece of the molecule together. • Consider CO2:

  21. 9.2 The Mole (Continued) • Molar mass of CO2 • Summing the molar masses Molar Mass 1 mol C atoms 12.011 g/mol 1 mol O atoms 15.999 g/mol 1 mol O atoms 15.999 g/mol 1 mol CO2 molecules 44.009 g/mol

  22. 9.2 The Mole (Continued) • Conversions with molar mass • 1 mole of water has a mass of 18.015 g/mol.

  23. 9.2 The Mole (Continued) How many moles of water are in 250.0 g of H2O?

  24. 9.2 The Mole (Continued) How many moles of water are in 250.0 g of H2O?

  25. 9.2 The Mole (Continued) How many grams of water are in 13.88 moles of water?

  26. 9.2 The Mole (Continued) How many grams of water are in 13.88 moles of water?

  27. 9.2 The Mole (Continued) Stoichiometry Conversions

  28. 9.3 Reaction Stoichiometry • Theoretical yield • Maximum amount of product that can be produced from a certain reactant amount

  29. 9.3 Reaction Stoichiometry (Continued) • Actual yield • Amount actually produced in a chemical reaction • Less than theoretical yield due to side reactions and side products • Conservation of mass is still observed.

  30. 9.3 Reaction Stoichiometry (Continued) • Percent yield • Percentage of theoretical yieldthat was isolated

  31. 9.3 Reaction Stoichiometry (Continued) What would be the percentage yield if 225.10 g of HI was isolated out of a possible 255.824 g HI?

  32. 9.3 Reaction Stoichiometry (Continued) What would be the percentage yield if 225.10 g of HI was isolated out of a possible 255.824 g HI? The percent yield would be 87.990%.

  33. 9.3 Reaction Stoichiometry (Continued) • Balanced equations can yield conversion factors: H2 + I2 2 HI

  34. 9.3 Reaction Stoichiometry (Continued) • Molecular formulas can also yield conversion factors:

  35. 9.3 Reaction Stoichiometry (Continued) Consider the following equation: 4 Al + 3 O2 2 Al2O3 • What would the conversion factor be between Al and O2? 2. What would the conversion factor be between O2 molecules and O atoms?

  36. 9.3 Reaction Stoichiometry (Continued) Consider the following equation: 4 Al + 3 O2 2 Al2O3 • What would the conversion factor be between Al and O2? 4 mol Al or 3 mol O2 3 mole O2 4 mol Al • What would the conversion factor be between O2 molecules and O atoms? 1 mol O2 or 2 atoms O 2 atoms O 1 mol O2

  37. 9.3 Reaction Stoichiometry (Continued) What mass of H2 would be required to make 10.0 g of HI?

  38. 9.3 Reaction Stoichiometry (Continued) What mass of H2 would be required to make 10.0 g of HI? g HI  moles HI  moles H2  g H2

  39. 9.3 Reaction Stoichiometry (Continued) What mass of H2 would be required to make 10.0 g of HI? First write the balanced equation Change grams of HI to moles HI Look at how many moles of H2 you get from that many moles of HI Change that to grams of H2 produced

  40. 9.3 Reaction Stoichiometry (Continued) What mass of H2 would be required to make 10.0 g of HI? g HI  moles HI  moles H2  g H2 Once the approach is known, complete the calculation: You find it will require 0.0788 g of H2.

  41. 9.3 Reaction Stoichiometry (Continued)

  42. 9.3 Reaction Stoichiometry (Continued) How many O atoms are in 10.7 g of oxygen, O2?

  43. 9.3 Reaction Stoichiometry (Continued) How many O atoms are in 10.7 g of oxygen, O2? g O2 moles O2  atoms O2

  44. 9.3 Reaction Stoichiometry (Continued) • Final advice

  45. 9.4 Dealing with a Limiting Reactant • Limiting reactant • Reactant that is in short supply • Limits the amount of product that can be made • Will be completely used up in a reaction • Excess reactant • Present in excess in a reaction • Will be left over after the reaction

  46. 9.4 Dealing with a Limiting Reactant (Continued) • Stoichiometric fashion reaction • Exact needed amount of each reactant present • Can use any reactant in calculating theoretical yield • Limiting fashion reaction • When a limited reactant is present • Must use limiting reactantin calculating theoretical yield.

  47. 9.4 Dealing with a Limiting Reactant (Continued) • Finding the limiting reactant • Write out the balanced equation. • Calculate the number of moles of each reactant. • Divide moles by the coefficient in the balanced equation. • The smallest mole-to-coefficient ratio is the limiting reactant.

  48. 9.4 Dealing with a Limiting Reactant (Continued) If you react 6 moles of propane with 29 moles of oxygen, what is the limiting reagent?

  49. 9.4 Dealing with a Limiting Reactant (Continued) If you react 6 moles of propane with 29 moles of oxygen, what is the limiting reagent? • C3H8 + 5 O2 3 CO2 + 4 H2O • 6 moles of C3H8 and 5 O2

  50. 9.4 Dealing with a Limiting Reactant (Continued)

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