1. 1 Chemical Reactions and Reaction Types

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 bonded is changed l Atoms aren’t created of destroyed. l Can be described several ways l In a sentence l Copper metal reacts with chlorine gas to form solid copper (II) chloride. l In a word equation Copper (s) + chlorine(g)  copper (II) chloride(s)

4. 4 Symbols used in equations Cu (s) + Cl 2 (g)  CuCl  (s) l the arrow separates the reactants from the products l Read “reacts to form” yields 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 Shows formulas and symbols for each reactant and product in a reaction l doesn’t indicate how many of each needed. l All chemical equations describe reactions.

9. 9 Convert these to skeleton equations l Solid iron (III) sulfide reacts with gaseous hydrogen chloride to form iron (III) chloride and hydrogen sulfide gas. Fe 2 S 3 (s) + HCl(g)  FeCl 3 (s) + H 2 S(g) 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. HNO 3 (aq) + Na 2 CO 3 (s)  NaNO 3 (aq) + H 2 O(l) + CO 2 (g) Now balance the equations.

10. 10 Balance the following: Fe(g) + O 2 (g)  Fe 2 O 3 (s) Cu(s) + AgNO 3 (aq)  Ag(s) + Cu(NO 3 ) 2 (aq) 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 atoms of each element on both sides of the equation.

13. 13 C + O 2  CO 2 l This equation is balanced C + O O  C O O

14. 14 C + O 2  CO We need one more oxygen in the products. Can’t change the formula, because it describes what is present. C + O  C O O A different reaction between carbon and oxygen.

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 (skeleton)  Count the number of atoms of each element appearing on both sides  Balance the elements one at a time by changing the coefficients (the numbers in front) Leave C H O until last.  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 If the number of atoms is odd and even on opposite sides multiply the odd to make even. AgNO 3 + Cu  Cu(NO 3 ) 2 + Ag (NO 3 on both sides treat as a single unit) 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 (or Composition) Reactions Combine - put together 2 elements, or compounds combine to make ONE compound (only one product). Ca(s) +O 2 (g)  CaO(s) SO 3 (g) + H 2 O(l)  H 2 SO 4 (aq) Predict the product if there 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(aq) Na(s) + Cl 2 (g) l CaCO 3 (s) CaO(s) + CO 2 (g)

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 (s) H 2 CO 3 (aq) 

35. 35 #3 Single Replacement l One element replaces another: a more active metal (or nonmetal) replaces a less active metal (or nonmetal) l Reactants must be an element and a compound. l Products will be a different element and a different compound. K (s) + NaCl (l)  Na (s) + KCl (l) (K more reactive than Na) F 2 (g) + LiCl (aq)  LiF (aq) + Cl 2 (g) (F more reactive than Cl)

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(s) + AlN(aq)  Zn(s) + HCl(aq)  l Think of water as HOH l Metals replace one of the H, combine with hydroxide. Na(s) + HOH(l) 

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 in your notes page 4 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 Predict if these reactions occur and if they do write the equation: Fe(s) + CuSO 4 (aq)  Pb(s) + KCl(aq)  Al(s) + HCl(aq) 

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 above. l Higher replaces lower. F 2 (g)+ HCl(aq)  Br 2 (l)+ KCl(aq) 

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

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 (aq) + NaOH (aq)  CuCl 2 (aq) + K 2 S (aq)  KOH (aq) + Fe(NO 3 ) 3 (aq)  (NH 4 ) 2 SO 4 (aq) + BaF 2 (aq) 

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(g) + O 2(g)  H 2 O(l)  Zn(s) + H 2 SO 4(aq)  HgO(s)  KBr(aq) +Cl 2(g)  AgNO 3(aq) + NaCl (aq)  Mg(OH) 2(aq) + H 2 SO 3(aq) 

46. 46 Last Type l Combustion is a reaction which involves a compound composed of only C H and maybe O reacting with oxygen gas from the air. l If the combustion is complete, the products will be CO 2 and H 2 O.

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

48. 48 Summary

49. 49 An equation l Describes a chemical reaction l Must be balanced because to follow 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.

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.