1. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 1 Chemical Stoichiometry Stoichiometry - The study of quantities of materials consumed and produced in chemical reactions.

2. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 2 Figure 3.1 Schematic Diagram of a Mass Spectrometer

3. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 3 Atomic Masses Elements occur in nature as mixtures of isotopes Carbon =98.89% 12 C 1.11% 13 C <0.01% 14 C Carbon atomic mass = 12.01 amu

4. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 4 Figure 3.2 Neon Gas

5. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 5 Figure 3.3 Mass Spectrum of Natural Copper

6. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 6 The Mole The number equal to the number of carbon atoms in exactly 12 grams of pure 12 C. 1 mole of anything = 6.022  10 23 units of that thing

7. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 7 Avogadro’s number equals 6.022  10 23 units

8. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 8 Molar Mass A substance’s molar mass (molecular weight) is the mass in grams of one mole of the compound. CO 2 = 44.01 grams per mole

9. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 9 Percent Composition Mass percent of an element: For iron in iron (III) oxide, (Fe 2 O 3 )

10. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 10 Figure 3.5 Schematic Diagram of the Combustion Device Used to Analyze Substances for Carbon and Hydrogen

11. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 11 Formulas molecular formula = (empirical formula) n [n = integer] molecular formula = C 6 H 6 = (CH) 6 empirical formula = CH

12. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 12 Empirical Formula Determination 1.Base calculation on 100 grams of compound. 2.Determine moles of each element in 100 grams of compound. 3.Divide each value of moles by the smallest of the values. 4.Multiply each number by an integer to obtain all whole numbers.

13. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 13 Chemical Equations Chemical change involves a reorganization of the atoms in one or more substances.

14. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 14 Chemical Equation A representation of a chemical reaction: C 2 H 5 OH + 3O 2  2CO 2 + 3H 2 O reactants products

15. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 15 Chemical Equation C 2 H 5 OH + 3O 2  2CO 2 + 3H 2 O The equation is balanced. 1 mole of ethanol reacts with 3 moles of oxygen to produce 2 moles of carbon dioxide and 3 moles of water

16. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 16 Calculating Masses of Reactants and Products 1.Balance the equation. 2.Write knowns and unknowns. 3.Include any other salient information. 4.Use mole ratios to calculate moles of desired substituent. 5.Convert moles to grams, if necessary.

17. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 17 Limiting Reactant The limiting reactant is the reactant that is consumed first, limiting the amounts of products formed.

18. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 18 Figure 3.9 Three Different Stoichiometric Mixtures of Methane and Water

19. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 19 Figure 3.10 Mixture of CH 4 and H 2 O Molecules

20. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 20 Figure 3.11 Methane and Water Reacting

21. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 21 Figure 3.12 Hydrogen and Nitrogen React to Form Ammonia According to the Equation N 2 + 3H 2  2NH 3

22. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 22 Solving a Stoichiometry Problem 1.Balance the equation. 2.Convert masses to moles. 3.Determine which reactant is limiting. 4.Use moles of limiting reactant and mole ratios to find moles of desired product. 5.Convert from moles to grams.