1. Chemical Equations & Reactions Chapter 8

2. Objectives List observations that suggest that a chemical reaction has taken place. List three requirements for a correctly written chemical equation. Write a word equation and a formula equation for a given chemical reaction. Balance a formula equation by inspection.

3. Chemical Reaction Process by which one or more substances are changed into one or more different substances

4. Indications of a Chemical Reaction 1. Evolution of heat & light

5. Indications of a Chemical Reaction 2. Production of a gas

6. Indications of a Chemical Reaction 3. Formation of a precipitate

7. Precipitate A solid that is produced as a result of a chemical reaction in solution & that separates from the solution

8. Indications of a chemical reaction 4. Change in color. (sumac leaves change color when chlorophyll is destroyed)

9. Chemical Equation Representation, with symbols and formulas, of the identities and relative amounts of the reactants and products in a chemical reaction Reactants  Products Follows the Law of Conservation of Mass

10. Characteristics of Chemical Equations The equation must represent known facts The equation must contain the correct formulas for the reactants & products The law of conservation of mass must be satisfied- which means the same # and type of atoms are present on both sides of the equation.

11. Word Equation Represents facts- only qualitative Example: Methane + oxygen  carbon dioxide + water Writing Chemical Equations

12. Example: CH 4(g) + O 2(g)  CO 2(g) + H 2 O (g) (not balanced) Symbols you will see in equations pg.266 Formula Equation Writing Chemical Equations

13. Inserting Coefficients-small whole # that appears in front of a formula Multiplies number of atoms of each element indicated in chemical formula Example: CH 4(g) + 2O 2(g)  CO 2(g) + 2H 2 O (g) Balanced Formula Equation Writing Chemical Equations

14. Balancing Chemical Equations Balance the formula equation according to the law of conservation of mass Balance the different types of atoms one at a time Balance polyatomic ions that appear on both sides of the equation as single units Balance H atoms and O atoms after atoms of all other elements have been balanced

15. Examples Mg + HCl  MgCl 2 + H 2 Al 2 (SO 4 ) 3 + Ca(OH) 2  Al(OH) 3 + CaSO 4 MgI 2 + KNO 3  KI + Mg(NO 3 ) 2

16. Writing and Balancing Equations from Word Equations 1. Write out correct chemical formulas and symbols. 2. Balance equation. Solid aluminum metal combines with oxygen gas to produce solid aluminum oxide

17. Writing equations from word equations Examples to try. 1. Solid calcium metal reacts with water to form aqueous calcium hydroxide and hydrogen gas. 2. Solid iron(III)oxide and carbon monoxide gas produces solid iron and carbon dioxide gas. 3. Solid copper reacts with aqueous silver nitrate to produce aqueous copper (II) nitrate and solid silver.

18. Objectives Define & give general equations for synthesis, decomposition, single- replacement, and double-replacement reactions. Classify a reaction as synthesis, decomposition, single displacement, double displacement or combustion. Predict the products of simple reactions if given the reactants.

19. 5 Basic Types of Reactions Synthesis Decomposition Single-replacement Double-replacement Combustion

20. Synthesis Reactions A reaction in which two or more substances combine to form a new compound A + X  AX A and X are elements or compounds AX is a compound

21. Synthesis Reactions Examples: magnesium + oxygen  __________ iron + oxygen  __________ calcium oxide + water  __________

22. Decomposition Reactions A reaction in which a single compound produces two or more simpler substances Opposite of synthesis reactions AX  A + X AX is a compound A and X are elements or compounds

23. Decomposition Reactions (Binary Compounds) Decomposition of a binary compound into its elements. Example: water  __________ + __________

24. Electrolysis The decomposition of a substance by an electric current

25. Decomposition Reactions (Metal Carbonates) Metal carbonates decompose to produce a metal oxide & carbon dioxide gas. Example: calcium carbonate  ______ + ______

26. Decomposition Reactions (Metal Hydroxides) Metal hydroxides (except group 1 metals) decompose to produce metal oxides & water. Example: calcium hydroxide  ______ + ______

27. Single-Replacement Reactions A reaction in which one element replaces a similar element in a compound A + BX  AX + B - or – Y + BX  BY + X A, B, X, Y are elements AX, BX, BY are compounds

28. Single-Replacement Reactions (Replacement of a Metal or Nonmetal) Example: aluminum + lead nitrate  ____ + ____ fluorine + sodium chloride  ____ + ____

29. Double-Replacement Reactions A reaction in which the ions of two compounds exchange places in an aqueous solution to form two new compounds AX + BY  AY + BX A, X, B, Y in reactants represent ions AY & BX represent ionic or molecular compounds

30. Double-Replacement Reactions (Formation of a Precipitate) One cation of one reactant combine with the anions of another reactant to form insoluble or slightly soluble compound Example: Potassium iodide + lead (II) nitrate  ____ + ____

31. Double-Replacement Reactions (Formation of a Gas) Example: Iron(II) sulfide + hydrochloric acid  ____ + ____

32. Double-Replacement Reactions (Formation of Water) Example: hydrochloric acid + sodium hydroxide  ____ + ____

33. Combustion Reactions A reaction in which a substance combines with oxygen, releasing a large amount of energy in the form of light and heat Combustion of a hydrocarbon always yield carbon dioxide and water.

34. Combustion Reactions Example: propane + oxygen  ____ + ____ (C 3 H 8 )

35. Try this: Write a balanced chemical equation for the following reaction: Ethyl alcohol (C 2 H 5 OH) burns to produce carbon dioxide and water.

36. Objectives Explain the significance of an activity series. Use an activity series to predict whether a given reaction will occur and what the products will be.

37. Activity Series A list of elements organized according to the ease with which the elements undergo certain chemical reactions Used to help predict whether certain chemical reactions will occur

38. Activity Series Table 8.3, p. 286 An element can replace any element below it but not above it Based on experiment Will be given to you on test.

39. Examples Using the activity series, predict whether each of the possible reactions will occur. For the reactions that will occur, write the products & balance the equation. Ba (s) + H 2 O (l)  Cu (s) + HBr (aq)  Al (s) + HBr (aq)  F 2(g) + NaCl (s) 