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Stoichiometry

Stoichiometry. The quantitative study of reactants and products in a chemical reaction. • Whether the units given for reactants or products are moles , grams , liters (for gases), or some other units, we use moles to calculate the amount of product formed in a reaction.

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Stoichiometry

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  1. Stoichiometry The quantitative study of reactants and products in a chemical reaction

  2. • Whether the units given for reactants or products are moles, grams, liters (for gases), or some other units, we use moles to calculate the amount of product formed in a reaction

  3. Known Unknown Stoichiometry Particles Particles Mass Moles Moles Mass Liters Liters

  4. Review before starting • The Mole • Molar Conversions • Balancing Chemical Equations

  5. Stoichiometry • Problem Types • Mole to Mole • Mole to Mass & Mass to Mole • Mass to Mass • Volume to Moles or Mass • Limiting Reactants & Per Cent Yield

  6. The Balanced Equation 2 CO(g) + O2 --> 2CO2(g) 2 moles 1 mole 2 moles Coefficients show relative amounts

  7. Mole Ratio A conversion factor that relates the amounts in moles of any two substances involved in a chemical reaction 2 CO(g) + O2--> 2 CO2(g) 2 moles of CO is equivalent to 2 moles of CO2 The mole ratio between CO and CO2 is 2:2 or 1:1 2mol CO 2 mol CO2 2 mol CO2 and 2 mol CO

  8. 140. grams of carbon monoxide reacts with an excess of oxygen gas to theoretically produce how many grams of carbon dioxide? CO(g) + O22 CO2(g) 140. g CO 1 mole CO 2 moles CO2 44.0 g CO2 = 220. g CO2 28.0 g CO 2 moles CO 1 mole CO2

  9. Known: 140 g CO Unknown: ? grams CO2 moles moles 5 moles CO 5 Moles CO2 mole bridge 20 Burlingame High School Chemistry

  10. Example Problem • If a furnace burns an amount of coal containing 6.0 moles of FeS2, how many moles of SO2 (an air pollutant) is theoretically produced? 4FeS2 + 11O2 2 Fe2O3 + 8 SO2 What is the mole ratio of FeS2 & SO2? 4 moles FeS2 : 8 moles SO2 4:8 or 1:2

  11. If a furnace burns an amount of coal containing 6.0 moles of FeS2, how many moles of SO2 (an air pollutant) is produced? 4FeS2 + 11O2 2 Fe2O3 + 8 SO2 Use the mole ratio - 4 molFeS2 to 8 SO2 = 12 mols SO2

  12. If a furnace burns an amount of coal containing 100.0g of FeS2, how many grams of SO2 (an air pollutant) is theoretically produced? Remember the balanced equation 4FeS2 + 11O2 2 Fe2O3 + 8 SO2

  13. 100.0 g FeS2

  14. 100.0 g FeS2 1 mole FeS2 120.0 g FeS2

  15. 100.0 g FeS2 1 mole FeS2 8 mole SO2 120.0 g FeS2 4 mole FeS2

  16. 100.0 g FeS2 1 mole FeS2 8 mole SO2 64.0 g SO2 120.0 g FeS2 4 mole FeS2 1 mole SO2

  17. 100.0 g FeS2 1 mole FeS2 8 mole SO2 64.0 g SO2 = 120.0 g FeS2 4 mole FeS2 1 mole SO2 51200 g SO2 480 = 106.67 g SO2 = 107 g SO2

  18. Number of Particles to Moles • How many atoms are present in 0.35 mol of Na?

  19. • How many atoms are present in 0.35 mol of Na? .35 molNa 6.02 x 1023 = 2.1 x 1023 atoms 1 mol

  20. • How many moles are present in 3.00 x 1021 molecules of C2H6? 3.00 x 1021molecules C2H6 1 mole C2H6 = 4.98 x 1 0-3 moles 6.02 x 1 023 molecules

  21. 2(6.02x1023) : (6.02x1 023) : 2(6.02x1 023) molecules molecules molecules 56g CO : 32 g O2 :88 g CO2 gases 2 volumes : 1 volume :2 volumes

  22. Volume Conversions Volume of a gas is dependent on the temperature & pressure In this unit we use Standard Temperature & Pressure (STP) for our problems STP = 00 Celsius & 1 atm of pressure

  23. A new conversion factor!! At SIP 1 mole of any gas occupies 22.4 Liters. 1 mole gas and 22.4 L 22.4 L 1 mole gas

  24. Volume Conversions If 5 g of magnesium is added to a solution of hydrochloric acid, what volume of hydrogen gas is produced at STP?

  25. Volume Conversions If 5.0 g of magnesium is added to a solution of hydrochloric acid, what volume of hydrogen gas is produced at STP? 1. Start with a balanced equation Mg(s) + 2HCl(aq)MgCl2(aq) + H2(g)

  26. If 5.0 g of magnesium is added to a solution of hydrochloric acid, what volume of hydrogen gas is produced at STP? Balanced equation Mg(s) + 2HCl(aq)MgCl2(aq) + H2(g) Dimensional Analysis 5.0g Mg 1 mol Mg 1 mol H222.4 L = 4.6L 24.3 g 1 mol Mg 1 mol H2 mass Mg mols Mg mols H2volume H2

  27. To make a dozen brownies the recipe calls for 2 cups flour, 112 grams chocolate, 25O ml water. You have 2 cups flour 50 grams chocolate, & 250 ml water If you want to make quality brownies you will make less than a dozen and have flour & water left over! What is the limiting reagent ?

  28. Zinc & Sulfur react to form zinc (II) sulÞde according to the following equation 8 Zn(s) + S88ZnS(s) If 2.00 mol of Zn are heated with 1.00 mole S8, identify the limiting reactant. How many moles of excess reactant will there

  29. Zinc & Sulfur react to form zinc (II) sulfide according to the following equation 8 Zn(s) + S88ZnS(s) If 2.00 mol of Zn are heated with 1 .00 mole S8, identify the limiting reactant? 2 mol Zn 1 mol S8 = .25 mole S8 8 mol Zn How many moles of excess reactant? Zn is limiting (there isn’t enough to react with all the S8)

  30. Zinc & Sulfur react to form zinc (II) sulfide according to the following equation 8 Zn(s) + S88ZnS(s) If 2.00 mol of Zn are heated with 1 .00 mole S8, identify the limiting reactant? 2 mol Zn 1 mol S8 = .25 mole S8 8 mol Zn How many moles of excess reactant? .75 moles of S8 Zn is limiting (there isn’t enough to react with all the S8)

  31. So far we have been doing stoichiometry • problems that represent theoretical yields • Actual Yield - the measured amount of • product that you really get in the reaction.

  32. Percent Yield • Percent Yield is the ratio of the actual yield • to the theoretical yield multiplied by 100 • Percent yield = actual yield x 100 • theoretical yield

  33. Quicklime, CaO, can be prepared by roasting • limestone, CaCO3, according to the following reaction. • CaCO3(s)CaO(s) + CO2(g) • When 2.00 x 1 03g of CaCO3(s) is heated the actual • yield of CaO is 1.05 x 1 03g. What is the percent yield?

  34. Percent Yield CaCO3(s)CaO(s) + CO2(g) Given: 2.00 x 1 03g of CaCO3(s) actual yield of CaO is 1.05 x 1 03g To solve Find theoretical yield (mass mass problem) Find percent yield (actual/theoretical x 1 00) 2.00 x 1 03g CaCO3(s) 1 mol CaCO3 1 mol CaO 56.0 g = 11 20g CaO 100.g 1 mol CaCO3 1 mol CaO Percent Yield = 1.05 x 103g x 100 = 93.8% 1.12 x 103g

  35. Quest Quest • Quest • 1. Na2SIO3 (s) + 8 HF(aq) - H2SiF6 (aq) + 2 NaF(aq) + 3 H2O (l) • How many moles of HF are needed to react with 0.300 mol of Na2SiO3? • How many grams of NaF form when 0.500 mol of HF reacts with excess Na2SiO3? • How many grams of Na2SiO3 can react with 0.800 g of HF? Quest Quest Quest

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