1. Chemical Reactions Potassium iodide (aq) reacts with lead nitrate (aq) producing a yellow precipitate of lead iodide

2. Chemical Formulas 1.Empirical formula 2.Molecular formula 3.Structural formula

3. Formulas? Empirical Metal and non-metal Ionic - lacking discrete unit, or molecule Simplest whole number ratio Metal and non-metal Ionic - lacking discrete unit, or molecule Simplest whole number ratio Covalent compounds Molecular and empirical formulas can be different –Glucose: molecular C 6 H 12 O 6 versus empirical CH 2 O. Covalent compounds Molecular and empirical formulas can be different –Glucose: molecular C 6 H 12 O 6 versus empirical CH 2 O. Molecular

4. Formula Weight General term ; Molecular Weight used more often “Sum” of the atomic weights of all the atoms in a chemical formula General term ; Molecular Weight used more often “Sum” of the atomic weights of all the atoms in a chemical formula

5. Hydrocarbons and Carbohydrates (Organic Chemistry) Hydrocarbons –Composed of H and C –Some simple ; some complex –Examples: C 3 H 8 (propane) C 4 H 10 (butane) –Complete “combustion” yields: CO 2, H 2 O + energy Carbohydrates –Composed of H, C, and O –Sugars, starches, cellulose –Examples: C 12 H 22 O 11 (sugar) –Complete “oxidation” yields: CO 2, H 2 O + energy. Hydrocarbons –Composed of H and C –Some simple ; some complex –Examples: C 3 H 8 (propane) C 4 H 10 (butane) –Complete “combustion” yields: CO 2, H 2 O + energy Carbohydrates –Composed of H, C, and O –Sugars, starches, cellulose –Examples: C 12 H 22 O 11 (sugar) –Complete “oxidation” yields: CO 2, H 2 O + energy.

6. Chemical Reactions Occur through formation and breaking of chemical bonds between atoms Involve changes in matter, creation of new materials, and energy exchange Chemical equations –Concise representation of chemical reactions. Occur through formation and breaking of chemical bonds between atoms Involve changes in matter, creation of new materials, and energy exchange Chemical equations –Concise representation of chemical reactions.

7. Chemical Equations Reactants - substances existing before reaction Products - substances existing after reaction Chemical symbols and formulas needed for quantitative purposes.

8. Balancing Equations Law of conservation of mass: atoms are neither created nor destroyed in chemical reactions –Mass of reactants = mass of products (i.e. balanced) To balance a chemical equation –Change coefficients in front of chemical formulas –Do not change the subscripts (numbers within formulas). Law of conservation of mass: atoms are neither created nor destroyed in chemical reactions –Mass of reactants = mass of products (i.e. balanced) To balance a chemical equation –Change coefficients in front of chemical formulas –Do not change the subscripts (numbers within formulas).

9. Subscripts vs Coefficients Fig 10.5

10. Example: Fig. 10.6

11. Stepwise balancing procedure page 279 Like an Inventory or “Bean Counting” 1.Law of conservation of mass (atoms are conserved) 2.Don’t change subscripts of formulas (compounds) 3.Multiply everything within a compound by the Coefficient Look for the most complex reactants and products –Try to balance atoms within them first Treat “Polyatomic” ions that appear on both sides as independent units with a charge Cross-over technique and use of fractional coefficients top find least common multiple to balance the equation –See the next few examples: 10.5, 10.6, and 10.7 Like an Inventory or “Bean Counting” 1.Law of conservation of mass (atoms are conserved) 2.Don’t change subscripts of formulas (compounds) 3.Multiply everything within a compound by the Coefficient Look for the most complex reactants and products –Try to balance atoms within them first Treat “Polyatomic” ions that appear on both sides as independent units with a charge Cross-over technique and use of fractional coefficients top find least common multiple to balance the equation –See the next few examples: 10.5, 10.6, and 10.7

15. Chemical Reactions Potassium iodide (aq) reacts with lead nitrate (aq) producing a yellow precipitate of lead iodide

16. Classifications of Chemical Reactions 1.Combination reactionsCombination reactions 2.Decomposition reactionsDecomposition reactions 3.Replacement reactionsReplacement reactions (1-3 = redox reaction subclasses) 4.Ion exchange reactionsIon exchange reactions 1.Combination reactionsCombination reactions 2.Decomposition reactionsDecomposition reactions 3.Replacement reactionsReplacement reactions (1-3 = redox reaction subclasses) 4.Ion exchange reactionsIon exchange reactions Bal Eq

17. Combination Reactions Rust: Fig 10.10 4 Fe (s) + 3 O 2(g) 2 Fe 2 O 3(s) Two or more substances combine to form a single compound

18. Decomposition Reactions Breakdown into simpler compounds or elements Usually require some form of energy for Rx to occur Breakdown into simpler compounds or elements Usually require some form of energy for Rx to occur 2 HgO (s) 2 Hg (s) + O 2 Δ

19. Example: Replacement Reaction 2 Al (s) + 3 CuCl 2 (aq) 2 AlCl 3 (aq) + 3 Cu (s) Fig 10.13

20. Replacement Reaction Fig 10.12 Occur because some elements have a stronger electron-holding ability More active metals (Li, K, Ca, Na) give up electrons to elements lower on the list Occur because some elements have a stronger electron-holding ability More active metals (Li, K, Ca, Na) give up electrons to elements lower on the list Ag (s) + CuCl 2 (aq) No Rx 2 Al (s) + 3 CuCl 2 (aq) 2 AlCl 3 (aq) + 3 Cu (s)

21. Ion Exchange Reaction AX + BY AY + BX 3 Ca(OH) 2 (aq) + Al 2 (SO 4 ) 3 (aq) 3 CaSO 4 (aq) + 2 Al(OH) 3 Ion Exchange: ions of one compound interact with ions of another compound Possible results: 1.Solid precipitates: ↓ 2.Gas forms: ↑ 3.Water formed: H 2 O ( l ) No ion exchange reaction occurred if both products are soluble (See appendix B) “ S ” versus “ i ” Ion Exchange: ions of one compound interact with ions of another compound Possible results: 1.Solid precipitates: ↓ 2.Gas forms: ↑ 3.Water formed: H 2 O ( l ) No ion exchange reaction occurred if both products are soluble (See appendix B) “ S ” versus “ i ”

26. Information from Chemical Equations Atoms are conserved Mass is conserved Law of combining volumes (gases) –Gases at the same temperature and pressure contain equal numbers of molecules Atoms are conserved Mass is conserved Law of combining volumes (gases) –Gases at the same temperature and pressure contain equal numbers of molecules

27. Units of Measurement used with Equations Atomic mass unit (u) = 1/12 th mass of carbon-12 One mole of a substance contains Avogadro’s number (6.02x10 23 ) of the basic chemical unit of that substance (atoms, molecules, ions, …) Example: A mole of carbon-12 atoms is defined as having 6.02 x 10 23 atoms totaling a mass of 12.00g Atomic mass unit (u) = 1/12 th mass of carbon-12 One mole of a substance contains Avogadro’s number (6.02x10 23 ) of the basic chemical unit of that substance (atoms, molecules, ions, …) Example: A mole of carbon-12 atoms is defined as having 6.02 x 10 23 atoms totaling a mass of 12.00g

28. Molar Weights Gram-atomic weight: mass in grams equal to atomic weight Gram-formula weight: mass in grams equal to formula weight Gram-molecular weight: mass in grams equal to molecular weight Gram-atomic weight: mass in grams equal to atomic weight Gram-formula weight: mass in grams equal to formula weight Gram-molecular weight: mass in grams equal to molecular weight

29. Quantitative use of Equations

30. Next Time: Water and Solutions