1. 1 Chapter 10 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 or destroyed. l Can be described several ways 1. In a sentence Copper reacts with chlorine to form copper (II) chloride. 2. 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 The arrow = “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 l shows that heat is supplied to the reaction l is used to indicate a catalyst is 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 Everyday Chemical Reactions

9. 9 Diatomic Elements l There are 7 elements that never want to be alone. l They form diatomic molecules. l H 2, N 2, O 2, F 2, Cl 2, Br 2, and I 2 l The –ogens and the –ines l 1 and 7 pattern on the periodic table l Dr. Brinclhof

10. 10 1 + 7 Pattern of Diatomics

11. 11 Third Type - Skeleton Equation l Uses formulas and symbols to describe a reaction l Skeleton doesn’t indicate how many of each compound is used Change this word equation into a skeleton equation - Iron(s) + chlorine(g)  iron(III) chloride(s) Fe(s) + Cl 2 (g)  FeCl 3 (s)

12. 12 Convert These to Skeleton Equations l Solid iron (III) sulfide reacts with gaseous hydrogen chloride to form solid 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.

13. 13 From Skeleton to Word Eq. Fe(s) + O 2 (g)  Fe 2 O 3 (s) Cu(s) + AgNO 3 (aq)  Ag(s) + Cu(NO 3 ) 2 (aq)

14. 14 Balancing Chemical Equations

15. 15 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. l Inventory polyatomics as individual atoms

16. 16 C + O 2  CO 2 l This equation is already balanced l What if it isn’t already? C + O O  C O O

17. 17 C + O 2  CO l We need one more oxygen in the products. l Can’t change the formula, because they follow the Law of Definite Proportions. C + O  C O O

18. 18 l Must be used to make another CO l But where did the other C come from? C + O  C O O O C

19. 19 l Must have started with two C 2 C + O 2  2 CO C + O  C O O O C C

20. 20 Rules for Balancing  Write the correct chemical 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) Save H and O until last!  Check to make sure it is balanced. 5. Simplify coefficients if possible

21. 21 Never, Never, 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 i.e. 2NaCl is okay, Na2Cl is not.

22. 22 Example H 2 +H2OH2OO2O2  Make a table to keep track of where you are at

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

24. 24 Example H 2 +H2OH2OO2O2  Changes the O RP H O 2 2 2 1 2

25. 25 Example H 2 +H2OH2OO2O2  Also changes the H RP H O 2 2 2 1 2 2

26. 26 Example H 2 +H2OH2OO2O2  Need twice as much H in the reactant RP H O 2 2 2 1 2 2 4

27. 27 Example H 2 +H2OH2OO2O2  Recount RP H O 2 2 2 1 2 2 4 2

28. 28 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

29. 29 Example H 2 +H2OH2OO2O2  This is the answer RP H O 2 2 2 1 2 2 4 2 4 Not this

30. 30 Techniques l If an atom appears more than once on a side, balance it last. l If you fix everything except one element, and it is even on one side and odd on the other, double the first number, then move on from there. If this is the last element to balance, then double all the coefficients. l C 4 H 10 + O 2  CO 2 + H 2 O

31. 31 Balance These Examples CH 4 + O 2  CO 2 + H 2 O 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

32. 32 Try to Balance These a) Pb(NO 3 ) 2 + K 2 CrO 4  PbCrO 4 + KNO 3 b) MnO 2 + HCl  MnCl 2 + H 2 O+ Cl 2 c) C 3 H 6 + O 2  CO 2 +H 2 O d) Zn(OH) 2 + H 3 PO 4  Zn 3 (PO 4 ) 2 + H 2 O e) CO + Fe 2 O 3  Fe + CO 2 f) CS 2 + Cl 2  CCl 4 +S 2 Cl 2 g) CH 4 + Br 2  CH 3 Br + HBr h) Ba(CN) 2 + H 2 SO 4  BaSO 4 + HCN

33. 33 Five Types of Reactions And Predicting the Products

34. 34 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. MovieMovie 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

35. 35 #1 Synthesis Reactions l Synthesis or Combination Reaction – To put together l 2 elements, or compounds combine to make one compound. A + B  AB is the general formula Ca + O 2  CaO SO 3 + H 2 O  H 2 SO 4 l We can predict the products if there are only two elements.

36. 36 Predict Products and Balance Mg + O 2  Ca + Cl 2  Fe + O 2  iron (III) oxide Al + O 2  l Remember that the first step is to write the correct formula l Then balance l Water production moviemovie

37. 37 #2 Decomposition Reactions l decompose = break apart l one reactant breaks apart into two or more elements or compounds. AB  A + B is the general formula l NaCl Na + Cl 2 l CaCO 3 CaO + CO 2

38. 38 #2 Decomposition Reactions l You 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

39. 39 #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 NiO + H 2 CO 3 (aq)  H 2 O +

40. 40 #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. A + BX  AX + B is general formula K + NaCl  Na + KCl F 2 + LiCl  LiF + Cl 2

41. 41 #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

42. 42 #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 

43. 43 #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 your handout l Higher on the list replaces lower l If the lone element is higher, it replaces compound- if lower, it doesn’t

44. 44 Activity Series l The more active element will replace the less active element in a chemical reaction. The K atom replaced Al in the previous example l The same is true for the more active halogens

45. 45 #3 Single Replacement l H can be replaced in acids by everything higher – Pb and above l Only the first 5 (Li - Na) react with water. Fe + CuSO 4  Pb + KCl  Al + HCl 

46. 46 #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 

47. 47 #4 Double Replacement l Two things replace each other. l Reactants must be two ionic compounds or acids. l Usually in aqueous solution AX + BY  AY + BX is general formula NaOH + FeCl 3  l Two positive ions (cation) change place NaOH + FeCl 3  Fe +3 OH - + Na +1 Cl -1 NaOH + FeCl 3  Fe(OH) 3 + NaCl

48. 48 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 

49. 49 How to Recognize Reaction l Look at the reactants l E + E Synthesis or Combination l CDecomposition l E + CSingle replacement l C + CDouble replacement

50. 50 Examples H 2 + O 2  H 2 O  Zn + H 2 SO 4  HgO  Mg(OH) 2 + H 2 SO 3  KBr +Cl 2  AgNO 3 + NaCl  Synthesis Decomposition Single Replacement Decomposition Double Replacement Single Replacement Double Replacement

51. 51 #5 Combustion l A compound typically composed of only C H and maybe O is reacted with oxygen. Movie – ethanol popper Movie 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. l Need for oxygen MovieMovie l Review Movie - 5 types of reactionsMovie

52. 52 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) l Movie – methane mamba Movie

53. 53 Distinguish between complete and incomplete combustion. Write a balanced equation for the complete combustion of each of these compounds. a) acetic acid, HC 2 H 3 O 2 c) glycerol, C 3 H 8 O 3 b) decane, C 10 H 22 d) sucrose, C 12 H 22 O 11 Write a balanced equation for the incomplete combustion of each of these compounds. a) glycerol, C 3 H 8 O 3 c) acetic acid, HC 2 H 3 O 2 b) glucose, C 6 H 12 O 6 d) acetylene, C 2 H 2

54. 54 Reaction Types and Balancing Equations Summary

55. 55 A Chemical Equation l Describes a reaction l Must be balanced because of the Law of Conservation of Mass l Can only be balanced by changing the coefficients. l Has special symbols to indicate state, and if catalyst or energy is required.

56. 56 Chemical Reactions l Come in 5 main types. l Can often tell what type they are by the type of reactants. l Single Replacement happens based on the activity series using activity chart. l Double Replacement typically happens if the product is a solid, water, or a gas.

57. 57 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. Homework

58. 58 Section 10.3 Reactions in Aqueous Solution l OBJECTIVES: –Write and balance net ionic equations.

59. 59 Net Ionic Equations l Many reactions occur in water- that is, in aqueous solution l Many ionic compounds “dissociate”, or separate, into cations and anions when dissolved in water l NaCl (s) dissolved in H 2 O Na + (aq) + Cl - (aq)

60. 60 Net Ionic Equations l Example: KI (aq) + AgNO 3(aq)  KNO 3(aq) + AgI (s) 1. Above the Full balanced equation 2. Below a Complete ionic equation K + (aq) + I - (aq) + Ag + (aq) + NO 3 - (aq) K + (aq) + NO 3 - (aq) + AgI (s)

61. 61 Net Ionic Equations 3. can be simplified by eliminating ions not directly involved (spectator ions) K + (aq) + I - (aq) + Ag + (aq) + NO 3 - (aq) K + (aq) + NO 3 - (aq) + AgI (s) Produces the Net ionic equation = I - (aq) + Ag + (aq) AgI (s)

62. 62 Predicting the Precipitate