1. PowerPoint Lectures to accompany Physical Science, 8e Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 10 Chemical Reactions Start

2. Core Concept Chemical symbols, formulas, and equations can be used to concisely represent elements, compounds, and what happens in a chemical reaction. –3 types of formulas

3. Chemical Formulas 1. Empirical formula –Identifies elements present in terms of simplest whole number ratios –Examples: table salt, NaCl; water, H 2 O 2.Molecular formula –Identifies actual number of atoms in a molecular compound –Example: water, H 2 O; not table salt, NaCl (ionic compound)

4. Chemical Formulas, cont. 3. Structural formula –Represents arrangement of atoms within a molecule –Related to 3-D structure of molecule

5. Empirical or Molecular Formula? Empirical Ionic - lacking discrete unit, or molecule Composed of both metallic and nonmetallic elements Electronegativity difference > 1.7 Molecular Covalent compounds Usually nonmetals bound to nonmetals Molecular and empirical formulas can be different –Glucose – molecular C 6 H 12 O 6 versus empirical CH 2 O

6. Molecular and Formula Weights Formula weight –Sum of atomic weights of all atoms in chemical formula Molecular weight –Formula weight of a molecular substance –Term often used for nonmolecular substances, as well

7. Percent Composition of Compounds Finding the mass percentage of an individual element from the formula weight

8. Percentage Composition Example

9. 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

10. Chemical Equations Reactants - substances existing before reaction Products - substances existing after reaction Word representation not sufficiently precise Chemical symbols and formulas needed for quantitative purposes

11. Balancing Equations Law of conservation of mass - atoms are neither created nor destroyed in chemical reactions Change coefficients in front of chemical formulas, not subscripts within formulas, to balance

12. Meaning of Subscripts and Coefficients with a Chemical Formula

13. Stepwise Balancing Procedure

14. Generalizing Equations Combustion reaction –A hydrocarbon in the presence of oxygen reacts to produce carbon dioxide and water. CH 4 + O 2  CO 2 + H 2 O

15. Alternative Classification 1.Combination reactions 2.Decomposition reactions 3.Replacement reactions (1-3 = redox reaction subclasses) 4.Ion exchange reactions

16. Oxidation – Reduction Reaction Oxidation – loss of electrons Reduction – gain of electrons

17. Combination Reactions Synthesis reaction in which two or more substances combine to form single compound X + Y  XY

18. Decomposition A compound is broken down into simpler substances XY  X + Y

19. Replacement Reactions An atom or polyatomic ion is replaced in a compound by a different atom or polyatomic ion.

20. Replacement Reactions Al (s) + CuCl 2(aq) → AlCl 3(aq) + Cu (s) 2Al (s) + 3CuCl 2(aq) → 2AlCl 3(aq) + 3Cu (s)

21. Ion Exchange Reactions A reaction that takes place when the ions of one compound interact with the ions of another compound forming –A solid precipitate –A gas –Water AX + BY  AY + BX

22. Ion Exchange Reactions __Ca(OH) 2(aq) + __Al 2 (SO 4 ) 3(aq)  __CaSO 4(aq) + __Al(OH) 3(s) 3 Ca(OH) 2(aq) + Al 2 (SO 4 ) 3(aq)  3 CaSO 4(aq) + 2 Al(OH) 3(s)

23. Information - 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

24. Units of Measurement Used with Equations Atomic mass unit = 1/12 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, …) A mole of carbon-12 atoms is defined as having a mass of 12.00g

25. 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

26. Quantitative Use of Equations Possible interpretations: 1.Molecular ratios of reactants and products 2.Mole ratios of reactants and products 3.Mass ratios of reactants and products