1. Chapter 8 Chemical Reactions

2. Getting Started The photograph in the textbook provides evidence that an exothermic chemical reaction is occurring. How would you convey to other scientists what is occurring in the photograph? A chemical equation is a shorthand way of communicating the reaction that is occurring. A chemical equation packs a great deal of information into relatively few symbols.

3. A chemical reaction is the process by which one or more substances are changed into one or more different substances. In any chemical reaction, the original substances are known as the reactants and the resulting substances are known as the products . According to the law of conservation of mass, the total mass of reactants must equal the total mass of products for any given chemical reaction.

7. Elements That Normally Exist as Diatomic Molecules

13. Additional Symbols Used in Chemical Equations

14. Additional Symbols Used in Chemical Equations

15. Symbols Used in Chemical Equations

17. Sample Problem A Solution The word equation must show the reactants, sodium oxide and water, to the left of the arrow. The product, sodium hydroxide, must appear to the right of the arrow. sodium oxide + water sodium hydroxide Sodium has an oxidation state of +1, that oxygen usually has an oxidation state of  2, and that a hydroxide ion has a charge of 1  . The unbalanced formula equation is Na 2 O + H 2 O NaOH (not balanced)

18. Adding symbols for the physical states of the reactants and products and the coefficient 2 in front of NaOH produces a balanced chemical equation . Na 2 O( s ) + H 2 O( l ) 2NaOH( aq )

19. Sample Problem B Translate the following chemical equation into a sentence: BaCl 2 ( aq ) + Na 2 CrO 4 ( aq ) BaCrO 4 ( s ) + 2NaCl( aq )

20. Sample Problem B Solution Aqueous solutions of barium chloride and sodium chromate react to produce a precipitate of barium chromate plus sodium chloride in aqueous solution.

29. Sample Problem C The reaction of zinc with aqueous hydrochloric acid produces a solution of zinc chloride and hydrogen gas. Write a balanced chemical equation for the reaction.

30. Sample Problem C Solution Write the word equation. zinc + hydrochloric acid zinc chloride + hydrogen Write the formula equation. Zn( s ) + HCl( aq ) ZnCl 2 ( aq ) + H 2 ( g ) (not balanced)

32. Sample Problem D Solid aluminum carbide, Al 4 C 3 , reacts with water to produce methane gas and solid aluminum hydroxide. Write a balanced chemical equation for this reaction.

33. Sample Problem D Solution The reactants are aluminum carbide and water. The products are methane and aluminum hydroxide. The formula equation is Al 4 C 3 ( s ) + H 2 O( l ) CH 4 ( g ) + Al(OH) 3 ( s ) (not balanced) Balance Al atoms Al 4 C 3 ( s ) + H 2 O( l ) CH 4 ( g ) + 4Al(OH) 3 ( s ) (partially balanced)

35. Count atoms to check balance. Al 4 C 3 ( s ) + 12H 2 O( l ) 3CH 4 ( g ) + 4Al(OH) 3 ( s ) (4Al + 3C) + (24H + 12O) = (3C + 12H) + (4Al + 12H + 12O) The equation is balanced.

37. Synthesis Reactions In a synthesis reaction, also known as a composition reaction, two or more substances combine to form a new compound. This type of reaction is represented by the following general equation. A + X AX A and X can be elements or compounds. AX is a compound

47. Decomposition Reactions Decomposition of Metal Carbonates Decomposition of Metal Chlorates Decomposition of Metal Hydroxides

49. Single-Displacement Reactions In a single-displacement reaction, also known as a replacement reaction, one element replaces a similar element in a compound. Many single-displacement reactions take place in aqueous solution. Single-displacement reactions can be represented by the following general equations. A + BX AX + B or Y + BX BY + X A, B, X, and Y are elements. AX, BX, and BY are compounds.

50. Displacement of a Metal in a Compound by Another Metal Aluminum is more active than lead. 2Al( s ) + 3Pb(NO 3 ) 2 ( aq ) 3Pb( s ) + 2Al(NO 3 ) 3 ( aq )

51. Displacement of Hydrogen in Water by a Metal The most-active metals, such as those in Group 1, react vigorously with water to produce metal hydroxides and hydrogen. 2Na( s ) + 2H 2 O( l ) 2NaOH( aq ) + H 2 ( g ) Less-active metals, such as iron, react with steam to form a metal oxide and hydrogen gas. 3Fe( s ) + 4H 2 O( g ) Fe 3 O 4 ( s ) + 4H 2 ( g )

52. Displacement of Hydrogen in an Acid by a Metal The more-active metals react with certain acidic solutions, such as hydrochloric acid and dilute sulfuric acid, replacing the hydrogen in the acid. The reaction products are a metal compound (a salt) and hydrogen gas. Mg( s ) + 2HCl( aq ) H 2 ( g ) + MgCl 2 ( aq )

54. Double-Displacement Reactions In double-displacement reactions, the ions of two compounds exchange places in an aqueous solution to form two new compounds. One of the compounds formed is usually a precipitate, an insoluble gas that bubbles out of the solution, or a molecular compound, usually water. The other compound is often soluble and remains dissolved in solution.

57. Double-Displacement Reactions Formation of a Gas FeS( s ) + 2HCl( aq ) H 2 S( g ) + FeCl 2 ( aq ) Formation of Water HCl( aq ) + NaOH( aq ) NaCl( aq ) + H 2 O( l )

59. Determining Reaction Types

60. Identifying Reactions and Predicting Products

61. Identifying Reactions and Predicting Products

62. Identifying Reactions and Predicting Products

65. Activity Series of the Elements