2. Chapter 16 Chemical Reactions

3. Objectives 16.1 Identify 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.

4. Objectives 16.3 Explain 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

5. 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

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7. 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

8. 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

9. How molecules are symbolized Cl 2 2Cl 2Cl 2 Molecules may also have brackets to indicate numbers of atoms. E.g. Ca(OH) 2 O H O H Ca 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

10. 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 CO 2 – Reactants: 4 C and 8 O – Products: 4 C and 8 O

11. 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 – C 4 O 8  C 8 O 16 is not allowed You may change the coefficient (# in front) – C 4 O 8  2 C 4 O 8 is allowed

12. 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  O 2 or N 2 In the reaction – CH 4 + O 2  CO 2 + H 2 O Balance O 2 last

13. Strategy 2) Write down the atoms and keep track of them like below – CH 4 + O 2  CO 2 + H 2 O Reactant  Product C __C __ H __H __ O __O __ As you add subscripts, change as you go

14. Balance equations by “inspection” Hints: start with elements that occur in one compound on each side. Treat polyatomic ions that repeat as if they were a single entity. 5 233.5 2746 222 263 C 2 H 6 + O 2  CO 2 + H 2 O a)P 4 + O 2  P 4 O 10 b)Li + H 2 O  H 2 + LiOH c)Bi(NO 3 ) 3 + K 2 S  Bi 2 S 3 + KNO 3 d)C 2 H 6 + O 2  CO 2 + H 2 O From Mg + O 2  MgO 2Mg + O 2  2MgO is correct Mg + ½O 2  MgO is incorrect Mg 2 + O 2  2MgO is incorrect 4Mg + 2O 2  4MgO is incorrect

15. Practice 1) Hydrogen and nitrogen react together to produce ammonia gas – H 2 + N 2  NH 3

16. 2) Butane burns in oxygen to produce carbon dioxide and steam (water vapour): C 4 H 10 + O 2  CO 2 + H 2 O

17. 3) When heated, aluminium reacts with solid copper oxide to produce copper metal and aluminium oxide: Al + CuO  Al 2 O 3 + Cu

18. 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: K 2 O + H 2 O  KOH

19. 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: Fe 2 (SO 4 ) 3 +KSCN  K 3 Fe(SCN) 6 + K 2 SO 4

20. a)Mg + HCl  MgCl 2 + H 2 b) Ca + N 2  Ca 3 N 2 c)NH 4 NO 3  N 2 O + H 2 O d) BiCl 3 + H 2 S  Bi 2 S 3 + HCl e) C 4 H 10 + O 2  CO 2 + H 2 O f) O 2 + C 6 H 12 O 6  CO 2 + H 2 O g) NO 2 + H 2 O  HNO 3 + NO h)Cr 2 (SO 4 ) 3 + NaOH  Cr(OH) 3 + Na 2 SO 4 i)Al 4 C 3 + H 2 O  CH 4 + Al(OH) 3 Balance these skeleton equations: 2 3 2 2 36 213 8 10 66 6 32 623 12 3 4

21. 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 38

22. Types: Synthesis Example C + O 2 OO C +  OO C OO C OO C O O C O O C O O C O O C O O C O O C O O C O O C O O C O O C O O C O O C General: A + B  AB

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

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

25. Types: Single displacement Example: Zn + CuCl 2  Zn Cl Cu + General: AB + C  AC + B Cl Zn Cu +

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

27. 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

28. a)Mg + HCl  MgCl 2 + H 2 b) Ca + N 2  Ca 3 N 2 c)NH 4 NO 3  N 2 O + H 2 O d) BiCl 3 + H 2 S  Bi 2 S 3 + HCl e) C 4 H 10 + O 2  CO 2 + H 2 O f) O 2 + C 6 H 12 O 6  CO 2 + H 2 O h)Cr 2 (SO 4 ) 3 + NaOH  Cr(OH) 3 + Na 2 SO 4 i)Al 4 C 3 + H 2 O  CH 4 + Al(OH) 3 What type of Reaction?

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

30. 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. K Na Li Ca Mg Al Zn Fe Ni Sn Pb H Cu Hg Ag Au

32. The most Reactive lithiumLi PotassiumK bariumBa calciumCa sodiumNa These metals displace hydrogen from water: Ca(s) + 2H 2 O(l)  Ca(OH) 2 + H 2 (g) These elements are very reactive and react readily to form compounds K Na Li Ca Mg Al Zn Fe Ni Sn Pb H Cu Hg Ag Au

33. The middle of the pack magnesiumMg aluminiumAl zincZn chromiumCr ironFe cadmiumCd nickelNi tinSn leadPb These metals displace hydrogen from acids: Zn(s) + HCl(aq)  ZnCl 2 + H 2 (g) K Na Li Ca Mg Al Zn Fe Ni Sn Pb H Cu Hg Ag Au

34. The Standard hydrogenH 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 K Na Li Ca Mg Al Zn Fe Ni Sn Pb H Cu Hg Ag Au

35. Unreactive copperCu silverAg mercuryHg platinumPt goldAu – 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. K Na Li Ca Mg Al Zn Fe Ni Sn Pb H Cu Hg Ag Au

36. 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 AgNO 3 (aq) → Cu(NO 3 ) 2 (aq) + 2 Ag(s) K Na Li Ca Mg Al Zn Fe Ni Sn Pb H Cu Hg Ag Au

37. 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(NO 3 ) 2 (aq) → 2 AgNO 3 (aq)+ (aq) + Zn (s) Since silver is below zinc on the chart, silver metal will not be 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.

38. Predict the products and balance these: (recall, metals above replace metals below, reactions with water yield metal hydroxides) Cu + Fe 2 (SO 4 ) 3 NR (no reaction) Zn + Li 2 CO 3 Cu + AlCl 3 K Na Li Ca Mg Al Zn Fe Ni Sn Pb H Cu Hg Ag Au Displacement Fe + CuSO 4  LiOH + H 2 Al 2 O 3 2 Ni+ NaCl  Al+ CuCl 2  Li+ ZnCO 3  Li + H 2 O  Al+O 2  33 3 2 23 2 ½ 222 324

39. 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)

40. 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

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