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Redox Reactions. Section 19.1 Oxidation and Reduction Section 19.2 Balancing Redox Equations. Click a hyperlink or folder tab to view the corresponding slides. Exit. Chapter Menu. Section 19.1 Oxidation and Reduction. Describe the processes of oxidation and reduction.

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  1. Redox Reactions Section 19.1Oxidation and Reduction Section 19.2Balancing Redox Equations Click a hyperlink or folder tab to view the corresponding slides. Exit Chapter Menu

  2. Section 19.1 Oxidation and Reduction • Describe the processes of oxidation and reduction. spectator ion: an ion that does not participate in a reaction and is not usually shown in an ionic equation • Identify oxidizing and reducing agents. • Determine the oxidation number of an element in a compound. • Interpret redox reactions in terms of change in oxidation state. Section 19-1

  3. Section 19.1 Oxidation and Reduction (cont.) oxidation-reduction reaction redox reaction oxidation reduction oxidizing agent reducing agent Oxidation and reduction are complementary—as an atom is oxidized, another atom is reduced. Section 19-1

  4. Electron Transfer and Redox Reactions • An oxidation-reduction reaction, or redox reaction involves the transfer of electrons from one atom to another. Section 19-1

  5. Electron Transfer and Redox Reactions (cont.) Section 19-1

  6. Electron Transfer and Redox Reactions (cont.) • Oxidationis defined as the loss of electrons from atoms of a substance. Na → Na+ + e– • Reduction is defined as the gain of electrons by the atoms of a substance. Cl2 + 2e– → 2Cl– Section 19-1

  7. Electron Transfer and Redox Reactions (cont.) • The oxidation number of an atom in an ionic compound is the number of electrons lost or gained by the atom when it forms an ion. • When an atom or ion is reduced, the numerical value of its oxidation number decreases. • When an atom or ion is oxidized, its oxidation number increases. Section 19-1

  8. Electron Transfer and Redox Reactions (cont.) • Oxidation numbers are tools that scientists use to keep track of the movement of electrons in a redox reaction. Section 19-1

  9. Oxidizing and Reducing Agents • The substance that oxidizes another substance by accepting its electrons is called an oxidizing agent. • The oxidizing agent is the substance that is reduced in a redox reaction. Section 19-1

  10. Oxidizing and Reducing Agents (cont.) • The substance that reduces another substance by losing its electrons is the reducing agent. • The reducing agent is the substance that is oxidized in a redox reaction. Section 19-1

  11. Redox and Electronegativity • Redox reactions are not limited to atoms of an element changing to ions. • Some redox reactions involve changes in molecular substances or polyatomic ions. N2(g) +3H2(g) → NH3(g) • N is reduced and H is oxidized. Section 19-1

  12. Redox and Electronegativity (cont.) • To determine which was oxidized and which was reduced, you must know which atom is more electronegative. • Elements with high electronegativity are strong oxidizing agents. Section 19-1

  13. Redox and Electronegativity (cont.) Section 19-1

  14. Determining Oxidation Numbers • To understand all types of redox reactions, the oxidation number of the atoms involved in the reaction must be determined. Section 19-1

  15. Determining Oxidation Numbers (cont.) Section 19-1

  16. Oxidation Numbers in Redox Reactions • Oxidation-reduction reactions are changes in oxidation number. • Atoms that are reduced have their oxidation number decreased. • Atoms that are oxidized have their oxidation number increased. Section 19-1

  17. Oxidation Numbers in Redox Reactions (cont.) Section 19-1

  18. A B C D Section 19.1 Assessment In a redox reaction, the reducing agent is: A.the substance that is reduced B.the substance that is oxidized C.the substance that gains electrons D.none of the above Section 19-1

  19. A B C D Section 19.1 Assessment In redox reactions, more electronegative elements tend to: A.be reduced B.be reducing agents C.lose electrons D.not change Section 19-1

  20. End of Section 19-1

  21. Section 19.2 Balancing Redox Reactions • Relate changes in oxidation number to the transfer of electrons. net ionic equation: an ionic equation that includes only the particles that participate in the reaction • Use changes in oxidation number to balance redox equations. • Balance net ionic redox equations using the oxidation-number method. Section 19-2

  22. Section 19.2 Balancing Redox Reactions (cont.) oxidation-number method species half-reaction Redox equations are balanced when the total increase in oxidation numbers equals the total decrease in oxidation numbers of the atoms involved in the reaction. Section 19-2

  23. The Oxidation-Number Method • Chemical equations must be balanced to show the correct quantities of reactants and products. • The number of electrons transferred from atoms must equal the number of electrons accepted by other atoms. Section 19-2

  24. The Oxidation-Number Method (cont.) • The total increase in oxidation numbers must equal the total decrease in oxidation numbers in the reaction. • This method is called the oxidation number method. Section 19-2

  25. Balancing Net Ionic Redox Equations • Sometimes it is preferred to express redox reactions in the simplest possible terms, showing only the oxidation and reduction processes. • When balancing equations in acidic solution, hydrogen ions (H+) or water molecules can be added to either side of the equation. • When balancing equations in basic solution, hydroxide ions (OH–) or water molecules can be added to either side of the equation. Section 19-2

  26. Balancing Redox Equations Using Half-Reactions • In chemistry, a species is any kind of chemical unit involved in a process. • Oxidation-reduction reactions occur whenever a species that can give up electrons comes in contact with another species that can accept them. Section 19-2

  27. Balancing Redox Equations Using Half-Reactions (cont.) • A half-reaction is one of the two parts of a redox reaction—the oxidation half of the reduction half. Section 19-2

  28. Balancing Redox Equations Using Half-Reactions (cont.) Section 19-2

  29. A B C D Section 19.2 Assessment A redox reaction split into two parts is called ____. A.net reaction B.oxidation-reaction C.half-reaction D.reduction-reaction Section 19-2

  30. A B C D Section 19.2 Assessment In acid solution, what would you use to balance the charge in a redox-reaction? A.electrons B.hydrogen ions and water C.hydroxide ions and water D.hydrogen ions and hydroxide ions Section 19-2

  31. End of Section 19-2

  32. Chemistry Online Study Guide Chapter Assessment Standardized Test Practice Image Bank Concepts in Motion Resources Menu

  33. Section 19.1 Oxidation and Reduction Key Concepts • Oxidation-reduction reactions involve the transfer of electrons from one atom to another. • When an atom or ion is reduced, its oxidation number is lowered. When an atom or ion is oxidized, its oxidation number is raised. • In oxidation-reduction reactions involving molecular compounds (and polyatomic ions with covalent bonds), the more-electronegative atoms are treated as if they are reduced. The less-electronegative atoms are treated as if they are oxidized. Study Guide 1

  34. Section 19.1 Oxidation and Reduction (cont.) Key Concepts Study Guide 1

  35. Section 19.2 Balancing Redox Equations Key Concepts • Redox equations in which the same element appears in several reactants and products can be difficult to balance using the conventional method. • The oxidation-number method is based on the number of electrons transferred from atoms equaling the number of electrons accepted by other atoms. • To balance equations for reactions in an acid solution, add enough hydrogen ions and water molecules to balance the equation. Study Guide 2

  36. Section 19.2 Balancing Redox Equations (cont.) Key Concepts • To balance equations for reactions in a basic solution, add enough hydroxide ions and water molecules to balance the equation. • A half-reaction is one of the two parts of a redox reaction. Study Guide 2

  37. A B C D What type of reaction involves the transfer of electrons from one atom to another? A.synthesis B.decomposition C.double replacement D.redox Chapter Assessment 1

  38. A B C D Less electronegative atoms in redox reactions are most often ____. A.oxidized B.reduced C.oxidizing agents D.neutral Chapter Assessment 2

  39. A B C D Any chemical unit involved in a process is called a(n) ____. A.atom B.type C.species D.ion Chapter Assessment 3

  40. A B C D Determine the oxidation number of oxygen in HNO3. A.+3 B.–3 C.+2 D.–2 Chapter Assessment 4

  41. A B C D Determine the oxidation number of nitrogen in HNO3. A.+1 B.+4 C.+5 D.–5 Chapter Assessment 5

  42. A B C D In the reaction MgI2 + Br2 → MgBr2 + I2, what is the oxidation number of I2? A.–1 B.+1 C.0 D.+½ STP 1

  43. A B C D Which is NOT an oxidizing agent in a redox reaction? A.substance reduced B.electron acceptor C.oxidizer of another substance D.electron donor STP 2

  44. A B C D How does the oxidation number change in sodium in the following equation? 2NaI(aq) + Cl2(aq) → 2NaCl(aq) + I2(aq) A.It changes from 0 to –1. B.It changes from –1 to 0. C.It changes from 2 to –2. D.no change STP 3

  45. A B C D If the temperature in a system is held constant, the pressure of a gas must do what when the volume is increased? A.no change B.increase C.decrease D.unable to determine STP 4

  46. A B C D What is the oxidizing agent in the following equation? Na2SO4 + 4C → Na2S + 4CO A.C B.S C.O D.Na STP 5

  47. Click on an image to enlarge. IB Menu

  48. IB 1

  49. IB 2

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