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Stoichiometry

CH. 9. Stoichiometry. A. Proportional Relationships. Ratio of eggs to cookies. I have 5 eggs. How many cookies can I make?. 2 1/4 c. flour 1 tsp. baking soda 1 tsp. salt 1 c. butter 3/4 c. sugar. 3/4 c. brown sugar 1 tsp vanilla extract 2 eggs 2 c. chocolate chips

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Stoichiometry

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  1. CH. 9 Stoichiometry

  2. A. Proportional Relationships Ratio of eggs to cookies • I have 5 eggs. How many cookies can I make? 2 1/4 c. flour 1 tsp. baking soda 1 tsp. salt 1 c. butter 3/4 c. sugar 3/4 c. brown sugar 1 tsp vanilla extract 2 eggs 2 c. chocolate chips Makes 5 dozen cookies. 5 eggs 5 doz. 2 eggs = 12.5 dozen cookies

  3. Proportional Relationships • Stoichiometry • mass relationships between substances in a chemical reaction • based on the mole ratio • Mole Ratio • indicated by coefficients in a balanced equation 2 Mg + O2 2 MgO

  4. Stoichiometry Steps 1. Write a balanced equation. 2. Identify known & unknown. 3. Line up conversion factors. • Mole ratio - moles  moles • Molar mass -moles  grams • Molar volume - moles  liters gas • Mole ratio - moles  moles Core step in all stoichiometry problems!! 4. Check answer.

  5. Conversions MASS IN GRAMS NUMBER OF PARTICLES MOLES Molar Mass (g/mol) 6.02  1023 particles/mol

  6. Stoichiometry Problems: Moles Only • How many moles of KClO3 must decompose in order to produce 9 moles of oxygen gas? 2KClO3 2KCl + 3O2 ? mol 9 mol 2 mol KClO3 3 mol O2 x mol KClO3 9 mol O2 = 2 mol KClO3 3 mol O2 9 mol O2 = 6 mol KClO3

  7. Stoichiometry Problems: Mass • How many grams of KClO3 must decompose in order to produce 9 grams of oxygen gas? 2KClO3 2KCl + 3O2 ? g 9 g a) Molar mass c) Molar mass b) Mole ratio Moles KClO3 Moles O2 Divide problem in steps

  8. a) Calculate O2 moles 2KClO3 2KCl + 3O2 ? g 9 g 1mol 32.0g 9.00 g = 0.281 mol O2

  9. b) Calculate KClO3 moles 2KClO3 2KCl + 3O2 ? mol 0.281 mol 2 mol KClO3 3 mol O2 x mol KClO3 0.281 mol O2 = 0.281 mol O2 2 mol KClO3 3 mol O2 = 0.187 mol KClO3

  10. c) Calculate KClO3 mass 0.187mol 122.55 g 1 mol = 22.9 g KClO3 2KClO3 2KCl + 3O2 22.9 g 9.00 g

  11. Stoichiometry Problems: density • How many grams of KClO3 must decompose in order to produce 6.3 mL of oxygen gas? (density of O2 1.429 g/mL) 2KClO3 2KCl + 3O2 ? g 6.3 mL a) Density Mass O2 d) Molar mass b) Molar mass c) Mole ratio Moles KClO3 Moles O2 Divide problem in steps

  12. a) Calculate O2 mass 2KClO3 2KCl + 3O2 ? g 9 g 1.426 g 1 mL 6.3 mL 9 g O2

  13. b) Calculate O2 moles 2KClO3 2KCl + 3O2 ? g 9 g 1mol 32.0g 9.00 g = 0.281 mol O2

  14. c) Calculate KClO3 moles 2KClO3 2KCl + 3O2 ? mol 0.281 mol 0.281 mol O2 2 mol KClO3 3 mol O2 = 0.187 mol KClO3

  15. d) Calculate KClO3 mass 0.187mol 122.55 g 1 mol = 22.9 g KClO3 2KClO3 2KCl + 3O2 22.9 g 6.3 mL

  16. Gas Stoichiometry StandardTemperature&Pressure 0°C and 1 atm • Moles  Liters of a Gas: • STP - use 22.4 L/mol • Non-STP - use ideal gas law 1 mol of a gas=22.4 L at STP

  17. Molar Volume at STP LITERS OF GAS AT STP Molar Volume (22.4 L/mol) MASS IN GRAMS NUMBER OF PARTICLES MOLES Molar Mass (g/mol) 6.02  1023 particles/mol

  18. Stoichiometry Problems: Volume • How many grams of KClO3 are req’d to produce 9.00 L of O2 at STP? 2KClO3 2KCl + 3O2 ? g 9 L a) Molar volume c) Molar mass b) Mole ratio Moles KClO3 Moles O2 Divide problem in steps

  19. a): Calculate O2 moles 2KClO3 2KCl + 3O2 ? g 9.00 L 1mol 22.4L 9.00 L = 0.4 mol O2

  20. b) Calculate KClO3 moles 2KClO3 2KCl + 3O2 ? mol 0.4 mol 2 mol KClO3 3 mol O2 x mol KClO3 0.4 mol O2 = 0.4 mol O2 2 mol KClO3 3 mol O2 = 0.27 mol KClO3

  21. c) Calculate KClO3 mass 0.27 mol 122.55 g 1 mol = 33 g KClO3 2KClO3 2KCl + 3O2 33 g 9.00 L

  22. Stoichiometry Problems: only gas reactions • 2 C2H2 (g) + 5 O2 (g)  4 CO2 (g) + 2 H2O (g) • If 79 L of carbon dioxide are produced in this reaction, how many liters of ethene (C2H2) were used? 2 L C2H2 4 L CO2 x L C2H2 78 L CO2 =

  23. Stoichiometry Problems: particles • How many grams of KClO3 are req’d to produce 9.044 x 1023 molecules of O2? 2KClO3 2KCl + 3O2 ? g 9.044 x 1023 molecules a) Avogadro’s number c) Molar mass b) Mole ratio Moles KClO3 Moles O2 Divide problem in steps

  24. Step 1: Calculate O2 moles 2KClO3 2KCl + 3O2 ? g 9.044 x 1023 molecules 9.044 x 1023molecules 1mol 6.022 x 1023molecules = 1.500 mol O2

  25. Step 2: Calculate KClO3 moles 2KClO3 2KCl + 3O2 ? mol 1.500 mol 2 mol KClO3 3 mol O2 x mol KClO3 1.500 mol O2 = 1.500 mol O2 2 mol KClO3 3 mol O2 = 1.00 mol KClO3

  26. Step 3: Calculate KClO3 mass 1.00 mol 122.55 g 1 mol = 122.55 g KClO3 2KClO3 2KCl + 3O2 122.33 g 9.044 x 1023 molecules

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