Chapter 16 Chemical Reactions

1. Chapter 16 Chemical Reactions

2. Objectives • 16.1Identify reactants and products in a chemical reaction • 16.1 Explain how a chemical reaction satisfies the law of conservation of mass • 16.1 Interpret chemical equations.

3. Objectives • 16.3Explain what is meant by a balanced chemical equation • 16.3 Demonstrate how to write balanced chemical equations • 16.4 Describe five types of chemical reactions using their generalized formulas

4. Objectives • 16.4 Classify various chemical reactions by type • 16.5 Differentiate between an exothermic and endothermic reaction • 16.5 Describe the effects of catalysts and inhibitors on the speed of chemical reactions

5. 33 Balancing Equations: Chemical

6. Overview • Reactants  Products • The reactants are changed into the products by the rearranging of atoms or changing state of matter. • Mass is conserved, atoms merely rearrange

7. Common Symbols • (s) = Solid • (l) = Liquid • (g) = Gas • (aq) = Aqueous (dissolved) • + = Plus (add the chemicals together) •  = Yields, or goes to make • Energy on Reactant = Endothermic • Energy on Product = Exothermic

8. Ca O O H H How molecules are symbolized Cl2 2Cl 2Cl2 • Molecules may also have brackets to indicate numbers of atoms. E.g. Ca(OH)2 • Notice that the OH is a group • The 2 refers to both H and O • How many of each atom are in the following? • a) NaOH • b) Ca(OH)2 • c) 3Ca(OH)2 Na = 1, O = 1, H = 1 Ca = 1, O = 2, H = 2 Ca = 3, O = 6, H = 6

9. Balanced Chemical Reaction • In a balanced chemical reactions, there are equal amounts of atoms on each side of the reaction • 4 C + 8 O  4 CO2 • Reactants: 4 C and 8 O • Products: 4 C and 8 O

10. Rules of Balancing • You may not change subscripts • The subscripts denote how many come with the molecule (or ionic ratio). If you change the subscript you are saying another type of molecule is reacting • C4O8C8O16 is not allowed • You may change the coefficient (# in front) • C4O8  2 C4O8is allowed

11. Strategy • You may or may not need to do the following, but if you are new to balancing, it may be helpful • 1) Balance atoms that are with only their same type of atom last O2 or N2 • In the reaction • CH4 + O2  CO2 + H2O • Balance O2 last

12. Strategy • 2) Write down the atoms and keep track of them like below • CH4 + O2  CO2 + H2O • Reactant  Product • C __ C __ • H __ H __ • O __ O __ • As you add subscripts, change as you go

13. Balance equations by “inspection” From Mg + O2 MgO 2Mg + O2 2MgO is correct Mg + ½O2 MgO is incorrect Mg2 + O2 2MgO is incorrect 4Mg + 2 O2 4MgO is incorrect Hints: start with elements that occur in one compound on each side. Treat polyatomic ions that repeat as if they were a single entity. 5 a) P4 + O2 P4O10 b) Li + H2O  H2+ LiOH c) Bi(NO3)3 + K2S Bi2S3 + KNO3 d) C2H6 + O2 CO2 + H2O 2 2 2 2 3 6 3.5 2 3 C2H6 + O2 CO2 + H2O 2 7 4 6

14. Practice • 1) Hydrogen and nitrogen react together to produce ammonia gas • H2 + N2 NH3

15. 2) Butane burns in oxygen to produce carbon dioxide and steam (water vapour): • C4H10 + O2 CO2 + H2O

16. 3) When heated, aluminium reacts with solid copper oxide to produce copper metal and aluminium oxide: • Al + CuO  Al2O3 + Cu

17. 4) Potassium oxide is not a stable compound. In the presence of water (or even water vapour in the air), it readily converts into potassium hydroxide: • K2O + H2O  KOH

18. In Word Form • 5) Iron (III) sulfate reacts with potassium thiocyanate to form an alum, which is a double salt consisting of a trivalent metal ion and a group I metal ion. In this case the alum is potassium iron(III) thiocyanate. The thiocyanate ion is formed from a carbon and a nitrogen atom (the standard cyanide ion) together with a sulphur atom: • Fe2(SO4)3 +KSCN  K3Fe(SCN)6 + K2SO4

19. Balance these skeleton equations: 2 a) Mg + HCl  MgCl2 + H2 b) Ca + N2 Ca3N2 c) NH4NO3 N2O + H2O d) BiCl3 + H2S  Bi2S3 + HCl e) C4H10 + O2 CO2 + H2O f) O2 + C6H12O6 CO2 + H2O g) NO2 + H2O  HNO3 + NO h) Cr2(SO4)3+ NaOH  Cr(OH)3+ Na2SO4 i) Al4C3 + H2O  CH4 + Al(OH)3 3 2 2 3 6 8 2 13 10 6 6 6 3 2 6 2 3 3 12 4

20. 38 Types of Chemical Reactions • Not every reaction is a combustion reaction (although many are) • Today’s goal is to learn 5 chemical reactions and be able to identify which one it is

21.  C C C C C C C C C C C C C C C C + O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O Types: Synthesis Example C + O2 General: A + B  AB

22.  + Na Na Cl Cl Types: Decomposition Example: NaCl General: AB  A + B

23. Hg Hg Hg Hg  + O O O O Types: Decomposition Example 2HgO General: AB  A + B

24. + +  Cl Cl Cl Cl Zn Zn Cu Cu Types: Single displacement Example: Zn + CuCl2 General: AB + C  AC + B

25. Ca Ca  + + Mg Mg S S O O Types: Double displacement Example: MgO + CaS General: AB + CD  AD + CB

26. The 5 reactions you must know (for now) combustion: AB + oxygen  oxides of A & B synthesis: A + B  C decomposition: AB  A + B single displacement: A + BC  AC + B double displacement: AB + CD  AD + CB

27. What type of Reaction? a) Mg + HCl MgCl2 + H2 b) Ca + N2 Ca3N2 c) NH4NO3 N2O + H2O d) BiCl3 + H2S  Bi2S3 + HCl e) C4H10 + O2 CO2 + H2O f) O2 + C6H12O6 CO2 + H2O h) Cr2(SO4)3+ NaOH Cr(OH)3+ Na2SO4 i) Al4C3 + H2O  CH4 + Al(OH)3

28. Activity Series of Metals Ionic Reactions with metals: Who gets to keep their electrons?

29. Displacement • Who wants their electrons more? • Some metals are more active than others and give up their electrons easier • Ie if a Sodium atom with a +1 charge runs into a neutral gold atom, who ends up with the charge?

31. lithium Li Potassium K barium Ba calcium Ca sodium Na These metals displace hydrogen from water: Ca(s) + 2H2O(l)  Ca(OH)2 + H2 (g) These elements are very reactive and react readily to form compounds The most Reactive

32. magnesium Mg aluminium Al zinc Zn chromium Cr iron Fe cadmium Cd nickel Ni tin Sn lead Pb These metals displace hydrogen from acids: Zn(s) + HCl(aq)  ZnCl2 + H2 (g) The middle of the pack

33. The Standard • hydrogen H • Everything is based off of Hydrogen • Who wins, Hydrogen or the metal for the battle for the electrons? • Hydrogen beats most of them except the ones on the next slide

34. copper Cu silver Ag mercury Hg platinum Pt gold Au Gold is the most unreactive metal These metals do not displace hydrogen from acids or water. These elements are more stable, and form compounds less readily than do those found higher in the table. Unreactive

35. How is this useful? • Predicting whether reactions happen or not • Any metal on the list can be oxidized by the ions of elements below it in the chart. For example copper is above silver in the chart. Thus, copper metal will be oxidized by silver ions as in the following example: • Cu(s) + 2 AgNO3 (aq) → Cu(NO3)2 (aq) + 2 Ag(s)

36. How is this useful? • Would it be possible to store a silver spoon in a zinc nitrate solution? That is, will the following reaction occur: • Ag(s) + Zn(NO3)2 (aq) → 2 AgNO3 (aq)+ (aq) + Zn (s) • Since silver is below zinc on the chart, silver metal will notbe oxidized by zinc. Therefore it would be safe to store the silver spoon in the zinc solution; the silver spoon will not undergo oxidation and corrode.

37. Displacement • Predict the products and balance these: (recall, metals above replace metals below, reactionswithwateryieldmetalhydroxides) Cu + Fe2(SO4)3 2 3 3 Fe + CuSO4  Ni + NaCl  NR (no reaction) 2 2 3 3 Al + CuCl2  Cu + AlCl3 Zn + Li2CO3 Li + ZnCO3  2 ½ 2 2 2 LiOH + H2 Li + H2O  Al + O2  4 3 2 Al2O3

38. Energy Changes • Most chemical reactions have a net loss or gain in thermal energy • Dictated by strength of bonds • Endothermic has strong chemical bonds on reactant side (hard to break) • Exothermic has strong chemical bonds on product side (form very strong bonds)

39. Catalyst • Speed up chemical reaction but are not part of the balanced chemical reaction • Example: Water is a catalyst for iron rusting • Special biological catalyst is called an enzyme

40. Inhibitors • Slow chemical reactions down • Example: Teachers keep students from enjoying themselves, slow down the fun