1. 1 Chapter 10-honors Chapter -CP Chemical Reactions

2. 2 All chemical reactions l have two parts l Reactants - the substances you start with l Products- the substances you end up with l The reactants turn into the products. Reactants  Products

3. 3 In a chemical reaction l The way atoms are joined is changed l Atoms aren’t created of destroyed. l Can be described several ways l In a sentence l Copper reacts with chlorine to form copper (II) chloride. l In a word equation Copper + chlorine  copper (II) chloride

4. 4 Symbols used in equations l the arrow separates the reactants from the products l Read “reacts to form” l The plus sign = “and” l (s) after the formula -solid l (g) after the formula -gas l (l) after the formula -liquid

5. 5 Symbols used in equations l (aq) after the formula - dissolved in water, an aqueous solution.  used after a product indicates a gas (same as (g))  used after a product indicates a solid (same as (s))

6. 6 Symbols used in equations l indicates a reversible reaction (More later) l shows that heat is supplied to the reaction l is used to indicate a catalyst used supplied, in this case, platinum.

7. 7 What is a catalyst? l A substance that speeds up a reaction without being changed by the reaction. l Enzymes are biological or protein catalysts.

8. 8 Skeleton Equation l Uses formulas and symbols to describe a reaction l doesn’t indicate how many. l All chemical equations are sentences that describe reactions.

9. 9 Convert these to equations l Solid iron (III) sulfide reacts with gaseous hydrogen chloride to form iron (II) chloride and hydrogen sulfide gas. l Nitric acid dissolved in water reacts with solid sodium carbonate to form liquid water and carbon dioxide gas and sodium nitrate dissolved in water.

10. 10 The other way Fe(g) + O 2 (g)  Fe 2 O 3 (s) Cu(s) + AgNO 3 (aq)  Ag(s) + Cu(NO 3 ) 2 (aq) l NO 2 N 2 (g) + O 2 (g)

11. 11 Balancing Chemical Equations

12. 12 Balanced Equation l Atoms can’t be created or destroyed l All the atoms we start with we must end up with l A balanced equation has the same number of each element on both sides of the equation.

13. 13 C + O 2  CO 2 l This equation is already balanced l What if it isn’t already? C + O O  C O O

14. 14 C + O 2  CO l We need one more oxygen in the products. l Can’t change the formula, because it describes what is C + O  C O O

15. 15 l Must be used to make another CO l But where did the other C come from? C + O  C O O O C

16. 16 l Must have started with two C 2 C + O 2  2 CO C + O  C O O O C C

17. 17 Rules for balancing  Write the correct formulas for all the reactants and products  Count the number of atoms of each type appearing on both sides  Balance the elements one at a time by adding coefficients (the numbers in front)  Check to make sure it is balanced.

18. 18 Never l Change a subscript to balance an equation. l If you change the formula you are describing a different reaction. l H 2 O is a different compound than H 2 O 2 l Never put a coefficient in the middle of a formula l 2 NaCl is okay, Na2Cl is not.

19. 19 Example H 2 +H2OH2OO2O2  Make a table to keep track of where you are at

20. 20 Example H 2 +H2OH2OO2O2  Need twice as much O in the product RP H O 2 2 2 1

21. 21 Example H 2 +H2OH2OO2O2  Changes the O RP H O 2 2 2 1 2

22. 22 Example H 2 +H2OH2OO2O2  Also changes the H RP H O 2 2 2 1 2 2

23. 23 Example H 2 +H2OH2OO2O2  Need twice as much H in the reactant RP H O 2 2 2 1 2 2 4

24. 24 Example H 2 +H2OH2OO2O2  Recount RP H O 2 2 2 1 2 2 4 2

25. 25 Example H 2 +H2OH2OO2O2  The equation is balanced, has the same number of each kind of atom on both sides RP H O 2 2 2 1 2 2 4 2 4

26. 26 Example H 2 +H2OH2OO2O2  This is the answer RP H O 2 2 2 1 2 2 4 2 4 Not this

27. 27 Examples AgNO 3 + Cu  Cu(NO 3 ) 2 + Ag Mg + N 2  Mg 3 N 2 P + O 2  P 4 O 10 Na + H 2 O  H 2 + NaOH CH 4 + O 2  CO 2 + H 2 O

28. 28 Types of Reactions Predicting the Products

29. 29 Types of Reactions l There are millions of reactions. l Can’t remember them all l Fall into several categories. l We will learn 5 types. l Will be able to predict the products. l For some we will be able to predict whether they will happen at all. l Will recognize them by the reactants

30. 30 #1 Combination Reactions l Combine - put together l 2 elements, or compounds combine to make one compound. Ca +O 2  CaO SO 3 + H 2 O  H 2 SO 4 l We can predict the products if they are two elements. Mg + N 2 

31. 31 Write and balance Ca + Cl 2  Fe + O 2  iron (II) oxide Al + O 2  l Remember that the first step is to write the formula l Then balance

32. 32 #2 Decomposition Reactions l decompose = fall apart l one reactant falls apart into two or more elements or compounds. l NaCl Na + Cl 2 l CaCO 3 CaO + CO 2

33. 33 #2 Decomposition Reactions l Can predict the products if it is a binary compound l Made up of only two elements l Falls apart into its elements lH2OlH2O l HgO

34. 34 #2 Decomposition Reactions l If the compound has more than two elements you must be given one of the products l The other product will be from the missing pieces l NiCO 3 H 2 CO 3 (aq) 

35. 35 #3 Single Replacement l One element replaces another l Reactants must be an element and a compound. l Products will be a different element and a different compound. Na + KCl  K + NaCl F 2 + LiCl  LiF + Cl 2

36. 36 #3 Single Replacement l Exceptions we’ve missed along the way l Zinc, Zn, always forms a +2 ion doesn’t need parenthesis l ZnCl 2 is zinc chloride l Silver, Ag, always forms a +1 ion l AgCl is silver chloride

37. 37 #3 Single Replacement l Metals replace metals (and hydrogen) K + AlN  Zn + HCl  l Think of water as HOH l Metals replace one of the H, combine with hydroxide. Na + HOH 

38. 38 #3 Single Replacement l We can tell whether a reaction will happen l Some are more active than other l More active replaces less active l There is a list on page 155 l Higher on the list replaces lower. l If the element by itself is higher, it happens, in lower it doesn’t

39. 39 #3 Single Replacement l Note the * l H can be replaced in acids by everything higher l Only the first 5 (Li - Na) react with water. Fe + CuSO 4  Pb + KCl  Al + HCl 

40. 40 #3 Single Replacement l What does it mean that Au And Ag are on the bottom of the list? l Nonmetals can replace other nonmetals l Limited to F 2, Cl 2, Br 2, I 2 l The order of activity is that on the table. l Higher replaces lower. F 2 + HCl  Br 2 + KCl 

41. 41 #4 Double Replacement l Two things replace each other. l Reactants must be two ionic compounds or acids. l Usually in aqueous solution NaOH + FeCl 3  l The positive ions change place. NaOH + FeCl 3  Fe +3 OH - + Na +1 Cl -1 NaOH + FeCl 3  Fe(OH) 3 + NaCl

42. 42 #4 Double Replacement l Will only happen if one of the products –doesn’t dissolve in water and forms a solid –or is a gas that bubbles out. –or is a covalent compound usually water.

43. 43 Complete and balance l assume all of the reactions take place. CaCl 2 + NaOH  CuCl 2 + K 2 S  KOH + Fe(NO 3 ) 3  (NH 4 ) 2 SO 4 + BaF 2 

44. 44 How to recognize which type l Look at the reactants l E + E Combination l CDecomposition l E + CSingle replacement l C + CDouble replacement

45. 45 Examples H 2 + O 2  H 2 O  Zn + H 2 SO 4  HgO  KBr +Cl 2  AgNO 3 + NaCl  Mg(OH) 2 + H 2 SO 3 

46. 46 Last Type l Combustion l A compound composed of only C H and maybe O is reacted with oxygen l If the combustion is complete, the products will be CO 2 and H 2 O. l If the combustion is incomplete, the products will be CO and H 2 O.

47. 47 Examples C 4 H 10 + O 2  (complete) C 4 H 10 + O 2  (incomplete) C 6 H 12 O 6 + O 2  (complete) C 8 H 8 +O 2  (incomplete)

48. 48 Chapter 7 Summary

49. 49 An equation l Describes a reaction l Must be balanced because to follow Law of Conservation of Energy l Can only be balanced by changing the coefficients. l Has special symbols to indicate state, and if catalyst or energy is required.

50. 50 Reactions l Come in 5 types. l Can tell what type they are by the reactants. l Single Replacement happens based on the activity series using activity series. l Double Replacement happens if the product is a solid, water, or a gas.

51. 51 The Process l Determine the type by looking at the reactants. l Put the pieces next to each other l Use charges to write the formulas l Use coefficients to balance the equation.

52. 52 Reactions in Aqueous Solutions l A solution contains one or more solutes (substance being dissolved)dissolved in water l Water is the solvent (substance doing the dissolving) l Aqueous solution is one in which water is the solvent.

53. 53 Aqueous Solutions l Molecular compounds can be the solutes in water. EX: l Ionic compounds can be the solutes in water. EX: l When two aq solutions that contain ions are combined, the ions may react with one another. These are always called DR rxns.

54. 54 Three types of Aqueous Rxns l Double replacement reactions can form three types of products 1) Precipitate= solid produced during a chemical reaction in solution. 2) Water 3) Gas

55. 55 Rxns that Produce Precipitates l Ionic equations differ from chemical equations because the substances are ions in solution and are written as ions in the equation. l Complete Ionic Equation: shows all particles in the equation as they really exist. l 2Na + (aq) + 2OH - (aq) + Cu 2+ (aq) + 2Cl -  2Na + (aq) + 2Cl - (aq) + Cu(OH) 2 (s)

56. 56 Cont. Precipitates l Since Cl - and Na + are reactants and products they do not participate in the reaction l Ions that do not participate are called SPECTATOR IONS. l The NET IONIC EQ omits the spectators. l 2Na + (aq) + 2OH - (aq) + Cu 2+ (aq) + 2Cl -  2Na + (aq) + 2Cl - (aq) + Cu(OH) 2 (s)

57. 57 Net Ionic Equation l Only OH - and Cu 2+ participate in the reaction l 2OH - (aq) + Cu 2+ (aq)  Cu(OH) 2 (s)

58. 58 Reactions that form Water l A Double Replacement reaction between an acid and a base. l An acid produces H+ ions in water. l A base produces OH- ions in water. l The water molecules produced in the reaction increase the number of solvent particles. l No visible evidence of a chemical rxn

59. 59 Example l Hydrobromic acid (aq) + sodium hydroxide(au) yields water(l) and sodium bromide(aq). l Write complete ionic equation l Write net ionic equation

60. 60 Reactions that form GAS l Double replacement that forms a gas l Common gases produced are CO 2, HCN, and H 2 S. l Hydroiodic acid(aq) + Lithium sulfide(aq) yields Hydrogen sulfide(g) + Lithium Iodide(aq). l Write complete ionic equation l Write net ionic equation.