1. ADVANCED CHEMISTRY Chapter 3 Stoichiometry

2. WHAT IS STOICHIOMETRY? Antoine Lavoisier observed that the total mass before a reaction is equal to the total mass after a reaction. This observation was termed the Law of Conservation of Mass

3. WHAT IS STOICHIOMETRY? Stoichiometry is the study of the quantitative nature of chemical reactions. It is used to balance chemical equations and determine molar mass and percent yield of products in chemical reactions.

4. TOPICS IN STOICHIOMETRY Balancing Chemical Equations Chemical Reactivity – types of reactions Weight, Mass and Mole Calculations Formula and Balanced Equation Analysis Limiting Reactants – Conclude w/Lab

5. BALANCING CHEMICAL EQUATIONS RECAP All forward equations are written with reactants of the left an products on the right Example: 2H 2 + O 2  2H 2 O Coefficient means 2 molecules of H 2, 4 atoms total Subscript means 2 atoms of H 4 atoms of H in product

6. BALANCING CHEMICAL EQUATIONS Atoms are neither created or destroyed…so all equations must be balanced! RULES FOR BALANCING EQUATIONS Cannot change subscripts Can change coefficients

7. BALANCING CHEMICAL EQUATIONS Examples – Balance this equation Na (s) + H 2 O (l)  NaOH (aq) + H 2(g) 2Na (s) + 2H 2 O (l)  2NaOH (aq) + H 2(g)

8. Patterns of Chemical Reactivity types of reactions We can use the periodic table to make predictions of chemical reactivity Elements in the same group react with other compounds in a similar way

9. Patterns of Chemical Reactivity types of reactions Example Alkali metals (group 1A elements) react with (OH) -, hydroxide, in similar way 2K (s) + 2H 2 O (l)  2KOH (aq) + H 2(g) 2Na (s) + 2H 2 O (l)  2NaOH (aq) + H 2(g)

10. Patterns of Chemical Reactivity types of reactions Combustion reactions – are rapid reactions that produce a flame Most of these reactions involve hydrocarbon compounds and oxygen as reactants and carbon dioxide and water are products Example: C 3 H 8(g) + 5O 2(g)  3CO 2(g) + 4H 2 O (l)

11. Combination and Decomposition Reactions Combination reactions – occur when two or more substances react to form one product Decomposition reactions – occur when one substance undergoes a reaction to produce two or more substances Patterns of Chemical Reactivity types of reactions For example..

12. Combination reactions A + B  C Patterns of Chemical Reactivity types of reactions Examples C (s) + O 2(g)  CO 2(g) N 2(g) + 3H 2(g)  2NH 3(g)

13. Decomposition reactions C  A + B Patterns of Chemical Reactivity types of reactions Examples CaCO 3(s)  CaO (s) + CO 2(g) 2NaN 3(s)  2Na (s) + 3N 2(g)

14. Sections 3.3 – 3.5 Section 3.3 Formula and Molecular Weights Average Atomic mass Percent Composition Section 3.4 The Mole Molar Mass The Mole, Interconverting Masses, Moles and # of Particles Section 3.5 Empirical Formula from Analysis Determining formulas through experimentation

15. The Atomic Mass Scale The atomic mass scale gives the mass of each element relative to the mass of 12C. The amu is defined by assigning a mass of 12 amu as the mass of a 12C atom. The atomic mass unit scale allows us to use a chemical formula to determine the percentage composition by mass of a compound. 1 amu = 1.66054 x 10 -24 g and 1g = 6.022 x 10 23 amu Section 3.3

16. Average Atomic mass

17. Weights and Mass Questions: Why is the term weight the proper tem to use? What’s the difference between Formula Weights and Molecular Weights?

18. Empirical and Molecular Weights

19. Mass % Occasionally, we must calculate the percentage composition of a compound For example, in order to verify the purity of the compound, we may wish to compare the calculated composition of a substance with that found experimentally.

20. The Mole Section 3.4 Just as a baker uses "dozen" to mean twelve, a chemist uses "mole" (abbreviated mol) to mean 6.022 x 10 23. Further, just as the word dozen can apply to any collection of twelve objects, the word mole can apply to any collection of 6.022 x 10 23 objects, whether they be atoms, molecules, or ions.

21. Conversions Conversions between mass, Moles and Numbers of particles

22. Practice problem #1 Calculate the number of C atoms in 0.350 mol of C 6 H 12 O 6

23. Practice problem #2 Calculate the mass, in grams, of 0.765 moles of Sodium Nitrate.

24. Empirical Formulas from Analysis What’s the difference between an Empirical Formula and a Molecular Formula? Section 3.5

25. Practice problem #3 A 5.325 g sample of methyl benzoate, a compound used in the manufacture of perfumes, is found to contain 3.758 g of carbon, 0.316 g of hydrogen, and 1.251 g of oxygen. What is the empirical formula of the substance?