1. Stoichiometry

2. I. Quantity in Chemical Reactions  (stoicheion) = element  (metreion) = measurement Stoichiometry = measurement of the quantities in chemical reactions

3. A. What goes in = what comes out Atoms aren’t created or destroyed, they just combine in different ways I. Quantity in Chemical Reactions

4. B. Ratios in chemical equations Coefficients of chemicals in balanced reactions show ratios between elements Example: 2H 2 O  2H 2 + O 2 Ratio: I. Quantity in Chemical Reactions 2 molecules H 2 O:2 molecules H 2 :1 molecule O 2

5. C. Using ratios Ratios can be used to determine unknown quantities from known quantities. I. Quantity in Chemical Reactions

6. C. Using ratios Example: 4Al + 3O 2  2Al 2 O 3 How many Al atoms are needed to fully react with 6 O 2 molecules? 4 atoms Al:3 molecules O 2 :2 compounds Al 2 O 3 4 atoms Al 3 molecules O 2 = x atoms Al 6 molecules O 2 (4 atoms Al) (3 molecules O 2 )(x atoms Al) (6 molecules O 2 ) = x atoms Al (4 atoms Al) (3 molecules O 2 ) (6 molecules O 2 ) = 8 atoms Al

7. C. Using ratios Example: 4Al + 3O 2  2Al 2 O 3 If you want 16 Al 2 O 3 compounds, how many Al atoms and how many O 2 molecules will you need? 4 atoms Al:3 molecules O 2 :2 compounds Al 2 O 3 4 atoms Al 2 comp. Al 2 O 3 = x atoms Al 16 comp. Al 2 O 3 (4 atoms Al) (2 comp. Al 2 O 3 )(x atoms Al) (16 comp. Al 2 O 3 ) = x atoms Al (4 atoms Al) (2 comp. Al 2 O 3 ) (16 comp. Al 2 O 3 ) = 32 atoms Al

8. D. Atoms aren’t a useful unit in the laboratory Instead of using atoms in the laboratory, we use larger quantities. Ratios only show relationships between numbers of chemicals – NOT mass or volume We can convert between mass, volume, number, and moles The ratio is the MOLAR RATIO I. Quantity in Chemical Reactions

9. Using ratios, take 2 Example: Mg + 2HCl  MgCl 2 + H 2 How many atoms of Mg are necessary to produce 6.02x10 23 compounds of MgCl 2 ? 1 atom Mg:2 comp. HCl :1 comp. MgCl 2 1 atom Mg 1 comp. MgCl 2 = x atoms Mg 6.02x10 23 comp. MgCl 2 (1 atom Mg) (1 comp. MgCl 2 )(x atoms Mg) (6.02x10 23 comp. MgCl 2 ) = x atoms Mg (1 atom Mg) (1 comp. MgCl 2 ) (6.02x10 23 comp. MgCl 2 ) = 6.02x10 23 atoms Mg :1 molecule H 2

10. Using ratios, take 2 Example: Mg + 2HCl  MgCl 2 + H 2 How many moles of Mg are necessary to produce 1 mole of MgCl 2 ? 1 mole Mg:2 moles HCl:1 mole MgCl 2 1 mole Mg 1 mole MgCl 2 = x moles Mg 1 mole MgCl 2 (1 mole Mg) (1 mole MgCl 2 )(x moles Mg) (1 mole MgCl 2 ) = 1 mole Mg (1 mole Mg) (1 mole MgCl 2 ) = x moles Mg :1 mole H 2

11. E. Solving Stoichiometric Problems In the reaction 2H 2 O 2  2H 2 O + O 2 how many moles of oxygen molecules are produced if I start with 17.3 moles of hydrogen peroxide (H 2 O 2 )? 2 moles H 2 O 2 :2 moles H 2 O:1 mole O 2 2 moles H 2 O 2 = x moles O 2 17.3 moles H 2 O 2 (1 mole O 2 ) (2 moles H 2 O 2 )(x moles O 2 ) (17.3 moles H 2 O 2 ) = 8.65 moles O 2 (1 mole O 2 ) (2 moles H 2 O 2 ) (17.3 moles H 2 O 2 ) = x moles O 2

12. E. Solving Stoichiometric Problems Ammonium nitrate breaks down to form dinitrogen monoxide and water. Write the equation and balance it: NH 4 NO 3  N2ON2O+H2OH2O2 2 N 4 H 3 OX3 X4 2 N 2 H 2 O

13. E. Solving Stoichiometric Problems How much ammonium nitrate is needed to form 55.56 moles of water? NH 4 NO 3  N 2 O + 2H 2 O 1 mole NH 4 NO 3 :1 mole N 2 O:2 moles H 2 O 1 mole NH 4 NO 3 = 55.56 moles H 2 O x moles NH 4 NO 3 27.78 moles NH 4 NO 3 (1 mole NH 4 NO 3 ) (2 moles H 2 O) (55.56 moles H 2 O) = (1 mole NH 4 NO 3 ) (2 moles H 2 O)(x moles NH 4 NO 3 ) (55.56 moles H 2 O) = x moles NH 4 NO 3