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Chapter 9

Quantities in Chemical Reactions. Chapter 9. Stoichiometry. Calculations involving chemical equations Chemical equations tell us exactly how much of one reactant will react (combine) with a second reactant and how much of the product we should expect. 2 Al + 6 HCl  2 AlCl 3 + 3 H 2.

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Chapter 9

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  1. Quantities in Chemical Reactions Chapter 9

  2. Stoichiometry • Calculations involving chemical equations • Chemical equations tell us exactly how much of one reactant will react (combine) with a second reactant and how much of the product we should expect.

  3. 2 Al + 6 HCl  2 AlCl3 + 3 H2 • 2 atom Al + 6 molecule HCl  2 formula unit AlCl3 + 3 molecule H2 • 2 mol Al + 6 mol HCl  2 mol AlCl3 +3 mol H2 • 2 (26.98 g) Al + 6 (36.46 g) HCl  2 (133.3 g) AlCl3 + 3 (2.016 g) H

  4. 2 Al + 6 HCl  2 AlCl3 + 3 H2 • How many molecules of HCl will react with 4 atoms of Al? • How many atoms of Al are required to make 1 molecule of AlCl3? • How many moles of H2 are made from 3 mole of HCl? • If 4 moles of AlCl3 are produced, how much H2 is produced? • How much HCl is required to react with 1 mole of Al?

  5. CH4 + 2 O2 CO2 + 2H2O • How many moles of oxygen are required to react completely with 50.0 g CH4? • What mass of CH4, in grams, is required to react with 96.0 g of O2? • Calculate the mass of CO2 that can be produced by burning 6.0 moles of CH4 in excess O2? • What mass of CH4 produces 3.01 x 1023 water molecules when burned in excess oxygen?

  6. Smelling salts contain ammonium carbonate, which can decompose to form ammonia, which acts as a mild heart stimulant. Ammonium carbonate decomposes by the reaction • (NH4)2CO3(s)  2 NH3(g) + CO2(g) + H2O(l) • How many g of NH3 will be formed from 0.500 g of (NH4)2CO3?

  7. Calculate the number of moles of calcium chloride needed to react with excess silver nitrate to produce 6.60 g of silver chloride. • 1st - write the equation ( a double displacement reaction) • 2nd -do stoichiometry

  8. Reactions and Energy •  Reactions will often generate energy (heat) or produce (give off) energy. We can use stoichiometry to calculate energy consumption or production.

  9. Exothermic reaction -- A reaction that liberates heat. • C6H12O6 2 C2H5OH + 2 CO2 + heat • Endothermic reaction -- A reaction that absorbs heat. • CO2 + heat  C + O2

  10. Consider the combustion of methane (used in our bunsen burners) • CH4(g) + 2 O2(g)  CO2(g) + 2 H2O(l) + 890 kJ • Calculate the amount of heat produced when 1.00 g of methane is burned in excess oxygen.

  11. Percent Yield • % Yield = (mass product/mass expected)*100(%) • What could cause the yield to be < 100%? • impurities in the sample • incomplete reaction • What could cause the yield to be > 100%? • unexpected reactions • Impure product • incorrect weighing etc.

  12. Copper(I)sulfide reacts upon heating in oxygen gas to produce copper metal and sulfur dioxide. How many grams of copper can be obtained from 500.0 g of cuprous sulfide using this process? • If 382.6 g of copper were obtained from the reaction above, what would be the percent yield? • What mass of sulfur dioxide would be produced from 500.0 grams of cuprous sulfide?

  13. Limiting reactant • Chez Ronald is making Big Macs. The formula for a Big Mac is B3M2, and is made according to the following fast food formula. • 2 M + 3 B  B3M2 • If Chez Ronald buys 28 meats and 36 buns how many Big Macs (B3M2) can he make? • We only got 11 Big Macs - What is the percent yield?

  14. 2 Mn(s) + 3 O2(g)  2 MnO3(s) • For the reaction above, compute the theoretical yield of product in moles for each of the following initial amounts of reactants. • 2 mol Mn; 2 mol O2 • 4.8 mol Mn; 8.5 mol O2

  15. How much potassium chloride is produced from the reaction of 2.00 g potassium and 3.00 g chlorine gas? Which is the limiting reagent? How much of the excess reagent remains? • We only recovered 3.66 g KCl. What is the percent yield?

  16. 4 Al(s) + 3 O2(g)  2 Al2O3(s) • For the reaction above, how many grams of Al2O3 will be formed from the reaction of 2.29 g of Al with 1.85 g of O2? • How many moles of each reactant remain after the reaction?

  17. When solutions containing 4.28 g Na2SO4 and 7.16 g of BaCl2 are mixed, what mass of BaSO4 is produced?

  18. Mg3N2+6H2O3Mg(OH)2+2NH3 • How many moles of Mg(OH)2 would be produced from the reaction of 0.10 mole of Mg3N2? • How many moles of NH3 would be produced from the reaction of 500 g of Mg3N2? • How many molecules of water would be required to react with 3.64 g of Mg3N2? • What is the maximum number of grams of Mg(OH)2 that can be produced by the reaction of 10.0 g of Mg3N2 and 14.4 g of H2O? • What is the percent yield if 9.4 g of Mg(OH)2 are produced?

  19. Ca5(PO4)3F+H2SO4+H2OH3PO4+CaSO4*2H2O+HF • Balance the reaction • How many moles water to react with 4.32 moles fluoroapatite? • How many grams of phosphoric acid will be formed from 493 g fluoroapatite, excess sulfuric acid and water? • How much calcium sulfate can be made from 5.00 g fluoroapatite, 5.00 g sulfuric acid, and 5.00 g water? How much of each reagent will remain? • If the above reaction yields 6.28 g of calcium phosphate dihydrate, what is the percent yield?

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