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Stoichiometry

Stoichiometry. Chemistry Dr. May. Moles. One mole of anything contains Avogadro’s number of particles: One mole of sodium (Na) contains 6.02 x 10 23 atoms with a mass of 23 grams One mole of water (H 2 O) contains 6.02 x 10 23 molecules and a mass of 18 grams.

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Stoichiometry

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  1. Stoichiometry Chemistry Dr. May

  2. Moles • One mole of anything contains Avogadro’s number of particles: • One mole of sodium (Na) contains 6.02 x 1023 atoms with a mass of 23 grams • One mole of water (H2O) contains • 6.02 x 1023 molecules and a mass of 18 grams

  3. Molar Mass (Molecular Weight) (MW) • Molar mass is the sum of the atomic masses of all the atoms in a molecule • The molar mass of H2O is (2+16) = 18 grams • The molar mass of CH4(methane) is (12 + 4) = 16 grams • The molar mass of CO2 is (12 + 32) = 44 grams • The molar mass of N2is (14 + 14) = 28 grams • 1 molar mass = 6.02 x 1023 molecules = 1 mole

  4. Molar Ratio • Zn + 2 HCl  ZnCl2 + H2 The molar ratio is: 1 : 2 : 1 : 1 • Or, 1 mole of zinc plus 2 moles of hydrochloric acid yields 1 mole of zinc chloride plus 1 mole of hydrogen gas

  5. Molar Ratio And Moles • Zn + 2 HCl  ZnCl2 + H2 1 : 2 : 1 : 1 • 1 mole of Zn has a mass of 65 grams • 2 moles of HCl has a mass of 72 grams • 1 mole of ZnCl2 has a mass of 135 grams • 1 mole of H2 has a mass of 2 grams

  6. Molar Ratio And Moles • Zn + 2 HCl  ZnCl2 + H2 • 1 mole of Zn has a mass of 65 grams • 2 moles of HCl has a mass of 72 grams 137 grams • 1 mole of ZnCl2 has a mass of 135 grams • 1 mole of H2 has a mass of _ 2 grams 137 grams

  7. Conservation Of Mass • In a balanced chemical equation, the total formula mass of the reactants must always equal the total formula mass of the products

  8. Moles And Mass Moles = Grams MW Grams = Moles x MW

  9. Grams = Moles x MW What is the mass of 1 mole of N2 ? What is the mass of 3 moles of H2 ? 2 x 14 = 28 grams 3 x 2 = 6 grams Mole-Mass Relationship

  10. Mole-Mole Relationships 3 H2 + N2 2 NH3 mr: 3 : 1 : 2 • 3 moles of H2 (6 grams) combines with • 1 mole of N2 (28 grams) to give • 2 moles of ammonia gas (34 grams) • 6 grams + 28 grams = 34 grams

  11. Mole-Mole Relationships 3 H2 + N2 2 NH3 mr: 3 : 1 : 2 moles: 6 2 4 • 6 moles of H2 (12 grams) combines with • 2 mole of N2 (56 grams) to give • 2 moles of ammonia gas (68 grams) • 12 grams + 56 grams = 68 grams

  12. Mole-Mole Relationships 3 H2 + N2 2 NH3 mr: 3 : 1 : 2 moles: 1.5 0.5 1 • 1.5 moles of H2 (3 grams) combines with • 0.5 moles of N2 (14 grams) to give • 1 mole of ammonia gas (17 grams) • 3 grams + 14 grams = 17 grams

  13. Mole-Mole Relationships 3 H2 + N2 2 NH3 mr: 3 : 1 : 2 moles: 1 0.33 0.67 • 1 mole of H2 (2 grams) combines with • 0.33 moles of N2 (9.3 grams) to give • 0.67 moles of ammonia gas (11.3 grams) • 2 grams + 9.3 grams = 11.3 grams

  14. Mole-Mole Relationships 3 H2 + N2 2 NH3 How many moles of nitrogen are needed to react completely with 3 moles of hydrogen ? The answer is …….. 1 mole

  15. Mole-Mole Relationships 3 H2 + N2 2 NH3 How many moles of nitrogen are needed to react completely with 1.5 moles of hydrogen ? The answer is …….. 0.5 moles

  16. Mole-Mole Relationships 3 H2 + N2 2 NH3 How many moles of nitrogen are needed to react completely with 6 moles of hydrogen ? The answer is …….. 2 moles

  17. Mole-Mole Relationships 3 H2 + N2 2 NH3 How many moles of ammonia do you get when 1 mole of nitrogen is reacted completely with 3 moles of hydrogen ? The answer is …….. 2 moles

  18. Stoichiometry (The Matrix) 3 1 2 0.17 0.5 0.33 1.0 4.7 5.7

  19. Mass-Mass Relationships 3 H2 + N2 2 NH3 How many grams of nitrogen are needed to react completely with 6 grams of hydrogen ? The answer is …….. 28 grams How did we know that ????

  20. Stoichiometry 3.0 1.0 2.0 28.0 6.0 34.0

  21. Mass-Mass Relationships 3 H2 + N2 2 NH3 How many grams of nitrogen are needed to react completely with 12 grams of hydrogen ? The answer is …….. 56 grams

  22. Mass-Mass Relationships 3 H2 + N2 2 NH3 How many grams of nitrogen are needed to react completely with 4.7 grams of hydrogen ? The answer is not obvious !

  23. Mass-Mass Relationships • Shall we go to our STOICHIOMETRY Matrix ???? • Away we go !!!!!!!

  24. Stoichiometry 2.35 2.35 0.78 Moles = grams MW 1.57 Grams = moles x MW 21.9 26.6

  25. Real Stoichiometry (The Equation) H2 + N2 NH3

  26. Real Stoichiometry (Balance Equation) 3 H2 + N2 2 NH3

  27. Real Stoichiometry (The Molar Ratio) 3 H2 + N2 2 NH3 3 1 2

  28. Real Stoichiometry (The Molar Mass) 2 28 17 3 H2 + N2 2 NH3 3 1 2

  29. Real Stoichiometry (The Problem) 2 28 17 3 H2 + N2 2 NH3 3 1 2 1.5 g.? • How many grams of NH3 are made when 1.5 grams H2 reacts completely with N2 ?

  30. Real Stoichiometry (Find Moles) 2 28 17 3 H2 + N2 2 NH3 3 1 2 Gr. 1.5 g. Moles ?? Moles = Grams MW Moles = 1.5  2 = 0.75

  31. Real Stoichiometry (Move Moles) 2 28 17 3 H2 + N2 2 NH3 3 1 2 Gr. 1.5 g. Moles 0.75            ? The molar ratio of NH3 to H2 is 2:3 The number of moles of NH3 is 2/3 of the moles of H2 2/3 of 0.75 = 0.50

  32. Real Stoichiometry (Find Grams) 2 28 17 3 H2 + N2 2 NH3 3 1 2 Gr. 1.5 g. ? Moles 0.75             0.50 Grams = moles x MW = 0.50 x 17 = 8.5

  33. Real Stoichiometry (The Answer) 2 28 17 3 H2 + N2 2 NH3 3 1 2 Gr. 1.5 g. 8.5 g. Moles 0.75             0.50 Grams = moles x MW = 0.50 x 17 = 8.5

  34. Real Stoichiometry (The Solution)) 2 28 17 3 H2 + N2 2 NH3 3 1 2 1.5 g.? • How many grams of NH3 are made when 1.5 grams H2 reacts completely with N2 ? • The answer is 8.5 grams

  35. The End • This presentation was created for the benefit of our students by the Science Department at Howard High School of Technology • Please send suggestions and comments to rmay@nccvt.k12.de.us

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