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 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

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 H 2 O is (2+16) = 18 grams The molar mass of CH 4 (methane) is (12 + 4) = 16 grams The molar mass of CO 2 is (12 + 32) = 44 grams The molar mass of N 2 is (14 + 14) = 28 grams 1 molar mass = 6.02 x 10 23 molecules = 1 mole

4. Molar Ratio Zn + 2 HCl  ZnCl 2 + H 2  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  ZnCl 2 + H 2 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 ZnCl 2 has a mass of 135 grams 1 mole of H 2 has a mass of 2 grams

6. Molar Ratio And Moles Zn + 2 HCl  ZnCl 2 + H 2  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 ZnCl 2 has a mass of 135 grams 1 mole of H 2 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. Mole-Mass Relationship Grams = Moles x MW What is the mass of 1 mole of N 2 ? What is the mass of 3 moles of H 2 ? 2 x 14 = 28 grams 3 x 2 = 6 grams

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

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

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

13. Mole-Mole Relationships 3 H 2 + N 2  2 NH 3  mr: 3 : 1 : 2 moles: 1 0.33 0.67 1 mole of H 2 (2 grams) combines with 0.33 moles of N 2 (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 H 2 + N 2  2 NH 3 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 H 2 + N 2  2 NH 3 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 H 2 + N 2  2 NH 3 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 H 2 + N 2  2 NH 3 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) MW22817 Eq.3 H 2 + N 2  2 NH 3 MR Moles grams 312 0.33 0.17 0.5 1.0 4.75.7

19. Mass-Mass Relationships 3 H 2 + N 2  2 NH 3 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 MW22817 Eq.3 H 2 + N 2  2 NH 3 MR312 Moles grams 6.0 28.0 2.01.03.0 34.0

21. Mass-Mass Relationships 3 H 2 + N 2  2 NH 3 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 H 2 + N 2  2 NH 3 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 MW22817 Eq. 3 H 2 + N 2  2 NH 3 MR312 Moles? grams4.7 Moles = grams MW 2.350.78 1.57 2.35 Grams = moles x MW 21.926.6

25. Real Stoichiometry (The Equation) H 2 + N 2  NH 3

26. Real Stoichiometry (Balance Equation) 3 H 2 + N 2  2 NH 3

27. Real Stoichiometry (The Molar Ratio) 3 H 2 + N 2  2 NH 3 3 1 2

28. Real Stoichiometry (The Molar Mass) 2 28 17 3 H 2 + N 2  2 NH 3 3 1 2

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

30. Real Stoichiometry (Find Moles) 2 28 17 3 H 2 + N 2  2 NH 3 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 H 2 + N 2  2 NH 3 3 1 2 Gr. 1.5 g. Moles 0.75            ? The molar ratio of NH 3 to H 2 is 2:3 The number of moles of NH 3 is 2/3 of the moles of H 2 2/3 of 0.75 = 0.50

32. Real Stoichiometry (Find Grams) 2 28 17 3 H 2 + N 2  2 NH 3 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 H 2 + N 2  2 NH 3 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 H 2 + N 2  2 NH 3 3 1 2 1.5 g. ? How many grams of NH 3 are made when 1.5 grams H 2 reacts completely with N 2 ? 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