1. 1 Chapter 6A Chemical Reactions

2. 2 CHAPTER OUTLINE  Chemical Reactions Chemical Reactions  Chemical Equation Chemical Equation  Balancing Equations Balancing Equations  Types of Chemical Reactions Types of Chemical Reactions  Double Replacement Reactions Double Replacement Reactions  Oxidation-Reduction Reactions Oxidation-Reduction Reactions  Redox in Biological Systems Redox in Biological Systems  Activity Series of Metals Activity Series of Metals

3. 3 CHEMICAL REACTIONS  A chemical reaction is a rearrangement of atoms in which some of the original bonds are broken and new bonds are formed to give different chemical structures.  In a chemical reaction, atoms are neither created, nor destroyed.  A chemical reaction, as described above, is supported by Dalton’s postulates.

4. 4 CHEMICAL REACTIONS 6 oxygen atoms = In a chemical reaction, atoms are neither created, nor destroyed

5. 5 CHEMICAL REACTIONS  A chemical reaction can be detected by one of the following evidences: 1. Change of color (formation of a solid) 2. Formation of a gas 3. Exchange of heat with surroundings

6. 6 CHEMICAL EQUATIONS  A chemical equation is a shorthand expression for a chemical reaction. Word equation: Aluminum combines with ferric oxide to form iron and aluminum oxide. Chemical equation: Al + Fe 2 O 3  Fe + Al 2 O 3

7. 7 CHEMICAL EQUATIONS  Reactants are separated from products by an arrow. Al + Fe 2 O 3  Fe + Al 2 O 3  Coefficients are placed in front of substances to balance the equation. 2 Al + Fe 2 O 3  2 Fe + Al 2 O 3 Subscripts

8. 8 CHEMICAL EQUATIONS  Reaction conditions are placed over the arrow. Al + Fe 2 O 3  Fe + Al 2 O 3  The physical state of the substances are indicated by the symbols (s), (l), (g), (aq). 2 Al (s) + Fe 2 O 3 (s)  2 Fe (l) + Al 2 O 3 (s)  heat solid liquid 

9. 9 BALANCING EQUATIONS  A balanced equation contains the same number of atoms on each side of the equation, and therefore obeys the law of conservation of mass.  Many equations are balanced by trial and error; but it must be remembered that coefficients can be changed in order to balance an equation, but not subscripts of a correct formula.

10. 10 BALANCING EQUATIONS  The general procedure for balancing equations is: Write the unbalanced equation: CH 4 + O 2  CO 2 + H 2 O Make sure the formula for each substance is correct

11. 11 BALANCING EQUATIONS  The general procedure for balancing equations is: Balance by inspection: CH 4 + O 2  CO 2 + H 2 O Count and compare each element on both sides of the equation 1 C= 4 H  2 H 2 O  3 O

12. 12 BALANCING EQUATIONS  Balance elements that appear only in one substance first. Balance H CH 4 + O 2  CO 2 + H 2 O 1 CH 4 + O 2  CO 2 + 2 H 2 O 4 H present on each side

13. 13 BALANCING EQUATIONS Balance O 1 CH 4 + O 2  CO 2 + 2 H 2 O 1 CH 4 + 2 O 2  CO 2 + 2 H 2 O 4 O present on each side When finally done, check for the smallest coefficients possible

14. 14 Examples: AgNO 3 + H 2 S  Ag 2 S + HNO 3 Al(OH) 3 + H 2 SO 4  Al 2 (SO 4 ) 3 + H 2 O Fe 3 O 4 + H 2  Fe + H 2 O C 4 H 10 + O 2  CO 2 + H 2 O 2 AgNO 3 + H 2 S  Ag 2 S + 2 HNO 3 2 Al(OH) 3 + 3 H 2 SO 4  Al 2 (SO 4 ) 3 + 6 H 2 O Fe 3 O 4 + 4 H 2  3 Fe + 4 H 2 O 2 C 4 H 10 + 13 O 2  8 CO 2 + 10 H 2 O

15. 15 CONCEPT CHECK  If red spheres represent oxygen atoms and blue spheres represent nitrogen atoms, write a balanced equation for the reaction shown below. 2 NO + O 2  2 NO 2

16. 16 TYPES OF CHEMICAL REACTIONS  Chemical reactions are classified into five types: 1. Synthesis or combination 2. Decomposition 3. Single replacement 4. Double replacement 5. Combustion

17. 17 SYNTHESIS or COMBINATION  In these reactions, 2 elements or compounds combine to form another compound. A + B  AB

18. 18 DECOMPOSITION  In these reactions, a compound breaks up to form 2 elements or simpler compound. AB  A +B

19. 19 SINGLE REPLACEMENT  In these reactions, a more reactive element replaces a less reactive element in a compound. A + BC  B + AC

20. 20 DOUBLE REPLACEMENT  In these reactions, two compounds combine to form two new compounds. AB + CD  AD + CB  The cation from one compound replaces the cation in another compound. + +

21. 21 COMBUSTION  A reaction that involves oxygen as a reactant and produces large amounts of heat is classified as a combustion reaction. CH 4 (g) + 2 O 2 (g)  CO 2 (g) + 2 H 2 O (g)

22. 22 Examples: Classify each of the reactions below: 1. Mg + CuCl 2  MgCl 2 + Cu 2. CaCO 3  CaO + CO 2 3. 2 HCl + Ca(OH) 2  CaCl 2 + 2 H 2 O 4. 4 Fe + 3 O 2  2 Fe 2 O 3 Single replacement Mg is more reactive than Cu Decomposition Double replacement Synthesis

23. 23 DOUBLE REPLACEMENT REACTIONS  Double replacement reactions can be subdivided into one the following subgroups: 1. Precipitation:formation of a solid 2. Neutralization:formation of water 3. Unstable product:formation of a gas

24. 24 PRECIPITATION REACTIONS  In these reactions one of the products formed is an insoluble solid called a precipitate.  For example, when solutions of potassium chromate, K 2 CrO 4, and barium nitrate, Ba(NO 3 ) 2, are combined an insoluble salt barium chromate, BaCrO 4, is formed. K 2 CrO 4 (aq) + Ba(NO 3 ) 2 (aq) BaCrO 4 (s) + 2 KNO 3 (aq) precipitate

25. 25 NEUTRALIZATION REACTIONS  The most important reaction of acids and bases is called neutralization.  In these reactions an acid combines with a base to form a salt and water. Acid Base Salt  Salts are ionic substances with the cation donated from the base and the anion donated from the acid.  In the laboratory, neutralization reactions are observed by an increase in temperature (exothermic reaction).

26. 26 UNSTABLE PRODUCT REACTIONS  Some chemical reactions produce gas because one of the products formed in the reaction is unstable.  Two such products are: H 2 CO 3 (aq)  CO 2 (g) + H 2 O (l) Carbonic acid: Sulfurous acid: H 2 SO 3 (aq)  SO 2 (g) + H 2 O (l)

27. 27 UNSTABLE PRODUCT REACTIONS  When either of these products appears in a chemical reaction, they should be replaced with their decomposition products. 2 HCl + Na 2 CO 3  2 NaCl + H 2 CO 3 2 HCl + Na 2 CO 3  2 NaCl + CO 2 (g) + H 2 O (l)

28. 28 Complete and balance each neutralization reaction below: Examples: HNO 3 + Ba(OH) 2  Ba(NO 3 ) 2 + H 2 O22 H 2 SO 4 + NaOH  Na 2 SO 4 + H 2 O22 HC 2 H 3 O 2 + KOH  KC 2 H 3 O 2 + H 2 O

29. 29 OXIDATION-REDUCTION REACTIONS  Reactions known as oxidation and reduction (redox) have many important applications in our everyday lives.  Rusting of a nail or the reaction within your car batteries are two examples of redox reactions.  In an oxidation-reduction reaction, electrons are transferred from one substance to another.  If one substance loses electrons, another substance must gain electrons.

30. 30 OXIDATION-REDUCTION REACTIONS  Oxidation is defined as loss of electrons, and reduction is defined as gain of electrons.  One way to remember these definitions is to use the following mnemonic:  Combination, decomposition, single replacement and combustion reactions are all examples of redox reactions. Oxidation Is Loss of electrons Reduction Is Gain of electrons OIL RIG

31. 31 OXIDATION-REDUCTION REACTIONS  In general, atoms of metals lose electrons to form cations, and are therefore oxidized, while atoms of non-metals gain electrons to form anions, and are therefore reduced. Ca + S CaS Ca Ca 2+ + 2 e - S + 2 e - S 2- Oxidation Reduction  For example, in the formation of calcium sulfide from calcium and sulfur  Therefore, the formation of calcium sulfide involves two half-reactions that occur simultaneously, one an oxidation and the other a reduction.

32. 32 OXIDATION-REDUCTION REACTIONS Mg + 2 HCl MgCl 2 + H 2 Mg Mg 2+ + 2 e - 2 H + + 2 e - H 2 Oxidation Reduction  Similarly, in the reaction of magnesium metal with hydrochloric acid In every oxidation-reduction reaction, the number of electrons lost must be equal to the number of electrons gained.

33. 33 OXIDATION-REDUCTION IN BIOLOGICAL SYSTEMS  Many important biological reactions involve oxidation and reduction.  In these reactions, oxidation involves addition of oxygen or loss of hydrogen, and reduction involves loss of oxygen or gain of hydrogen.  For example, poisonous methyl alcohol is metabolized by the body by the following reaction: CH 3 OH H 2 CO + 2H methyl alcoholformaldehyde Oxidation (loss of hydrogen)

34. 34 OXIDATION-REDUCTION IN BIOLOGICAL SYSTEMS  The formaldehyde is further oxidized to formic acid and finally carbon dioxide and water by the following reactions: 2 H 2 CO + O 2 2H 2 CO 2 formic acidformaldehyde Oxidation (gain of oxygen) formic acid 2 H 2 CO 2 + O 2 CO 2 + H 2 O

35. 35  In many biochemical oxidation-reduction reactions, the transfer of hydrogen atoms produces energy in the cells.  For example, cellular respiration is an oxidation- reduction process that transfers energy from the bonds in glucose to form ATP. OXIDATION-REDUCTION IN BIOLOGICAL SYSTEMS C 6 H 12 O 6 + 6 O 2 6 CO 2 + 6 H 2 O + ATP + Heat

36. Glucose  Heat C 6 H 12 O 6 O2O2 CO 2 H2OH2O ATP 6 6 6 Loss of hydrogen atoms (becomes oxidized) Gain of hydrogen atoms (becomes reduced) OXIDATION-REDUCTION IN BIOLOGICAL SYSTEMS

37. 37 OXIDATION-REDUCTION IN BIOLOGICAL SYSTEMS  The oxidation of a typical biochemical molecule can involve the transfer of hydrogen atoms to a proton acceptor such as coenzyme FAD to produce its reduced form FADH 2.

38. 38 REDOX IN BIOLOGICAL SYSTEMS  In summary, the particular definition of oxidation- reduction depends on the process that occurs in the reaction.  A summary of these definitions appears below:

39. 39 Example 1: Linoleic acid, an unsaturated fatty acid, can be converted to a saturated fatty acid by the reaction shown below. Is linoleic acid oxidized or reduced in this reaction? C 18 H 32 O 2 + 2 H 2 C 18 H 36 O 2 Gain of hydrogen Reduction

40. 40 Example 2: The reaction of succinic acid (C 4 H 6 O 4 ) provides energy for the ATP synthesis and is shown below: a)Is succinic acid oxidized or reduced? b)Is FAD oxidized or reduced? C 4 H 6 O 4 C 4 H 4 O 4 + 2 H Loss of hydrogen Gain of hydrogen FAD + 2 H FADH 2 oxidation reduction

41. 41 ENZYMES IN BIOLOGICAL SYSTEMS  In biochemical reactions, enzymes are necessary to oxidize glucose and other foods.  For example, oxidation of glucose involves the transfer of hydrogen atoms and electrons to an enzyme, such as NAD + to produce its reduced form NADH.

42. 42 ENZYMES IN BIOLOGICAL SYSTEMS  Similarly, oxidation of methanol involves transfer of 2 hydrogen atoms and 2 electrons to NAD + to form the reduced form NADH.

43. 43 ENZYMES IN BIOLOGICAL SYSTEMS  Molecules such as NAD + are called “electron carriers” since they carry electrons in their reduced form.  The electron carriers collectively are called electron transport chain.  As electrons are transported down the chain, ATP is generated.

44. 44 ENZYMES IN BIOLOGICAL SYSTEMS

45. 45 ACTIVITY SERIES OF METALS  Activity series is a listing of metallic elements in descending order of reactivity.  Hydrogen is also included in the series since it behaves similar to metals.  Activity series tables are available in textbooks and other sources.

46. 46 ACTIVITY SERIES OF METALS  Elements listed higher will displace any elements listed below them.  For example Na will displace any elements listed below it from one of its compounds. 2 Na (s) + MgCl 2 (aq)  2 NaCl (aq) + Mg (s) Na (s) + AgCl (aq)  NaCl (aq) + Ag (s)

47. 47 ACTIVITY SERIES OF METALS  Elements listed lower will not displace any elements listed above them.  For example Ag cannot displace any elements listed above it from one of its compounds. Ag (s) + CuCl 2 (aq)  No Reaction Ag (s) + HCl (aq)  No Reaction

48. 48 Example 1: Use activity series to complete each reaction below. If no reaction occurs, write “No Reaction”. Pb (s) + HCl (aq)  Metals Fe Ni Sn Pb H Cu Ag Pb is more reactive than H PbCl 2 (aq) + H 2 (g)2

49. 49 Example 2: Use activity series to complete each reaction below. If no reaction occurs, write “No Reaction”. Zn (s) + MgCl 2 (aq)  Metals Na Mg Al Zn Fe Ni Zn is less reactive than Mg No Reaction

50. 50 Example 3: Use activity series to complete each reaction below. If no reaction occurs, write “No Reaction”. Ni (s) + CuCl 2 (aq)  Metals Fe Ni Sn Pb H Cu Ag Ni is more reactive than Cu NiCl 2 (aq) + Cu (s)

51. 51 Example 4: Use activity series to complete each reaction below. If no reaction occurs, write “No Reaction”. Mg (s) + AlCl 3 (aq)  Metals Na Mg Al Zn Fe Ni Mg is more reactive than Al MgCl 2 (aq) + Al (s)2332

52. 52 THE END