1. CHEMISTRY Matter and Change
Chapter 19: Redox Reactions

2. Section 19.1 Oxidation and Reduction
CHAPTER19
Table Of Contents
Section 19.1 Oxidation and Reduction
Section Balancing Redox Equations
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3. Oxidation and Reduction
SECTION19.1
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.

4. Oxidation and Reduction
SECTION19.1
Oxidation and Reduction
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.

5. Oxidation and Reduction
SECTION19.1
Oxidation and Reduction
Electron Transfer and Redox Reactions
An oxidation-reduction reaction, or redox reaction involves the transfer of electrons from one atom to another.

6. Oxidation and Reduction
SECTION19.1
Oxidation and Reduction
Electron Transfer and Redox Reactions (cont.)

7. Oxidation and Reduction
SECTION19.1
Oxidation and Reduction
Electron Transfer and Redox Reactions (cont.)
Oxidation is 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–

8. Oxidation and Reduction
SECTION19.1
Oxidation and Reduction
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.

9. Oxidation and Reduction
SECTION19.1
Oxidation and Reduction
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.

10. Oxidation and Reduction
SECTION19.1
Oxidation and Reduction
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.

11. Oxidation and Reduction
SECTION19.1
Oxidation and Reduction
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.

12. Oxidation and Reduction
SECTION19.1
Oxidation and Reduction
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.

13. Oxidation and Reduction
SECTION19.1
Oxidation and Reduction
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.

14. Oxidation and Reduction
SECTION19.1
Oxidation and Reduction
Redox and Electronegativity (cont.)

15. Oxidation and Reduction
SECTION19.1
Oxidation and Reduction
Determining Oxidation Numbers
To understand all types of redox reactions, the oxidation number of the atoms involved in the reaction must be determined.

16. Oxidation and Reduction
SECTION19.1
Oxidation and Reduction
Determining Oxidation Numbers (cont.)

17. Oxidation and Reduction
SECTION19.1
Oxidation and Reduction
Oxidation Numbers in Redox Reactions
Oxidation-reduction reactions feature changes in oxidation number.
Atoms that are reduced have their oxidation number decreased.
Atoms that are oxidized have their oxidation number increased.

18. Oxidation and Reduction
SECTION19.1
Oxidation and Reduction
Oxidation Numbers in Redox Reactions (cont.)

19. In a redox reaction, the reducing agent is:
SECTION19.1
Section Check
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

20. In redox reactions, more electronegative elements tend to:
SECTION19.1
Section Check
In redox reactions, more electronegative elements tend to:
A. be reduced
B. be reducing agents
C. lose electrons
D. not change

22. Balancing Redox Reactions
SECTION19.2
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.

23. Balancing Redox Reactions
SECTION19.2
Balancing Redox Reactions
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.

24. Balancing Redox Reactions
SECTION19.2
Balancing Redox Reactions
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.

25. Balancing Redox Reactions
SECTION19.2
Balancing Redox Reactions
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.

26. Balancing Redox Reactions
SECTION19.2
Balancing Redox Reactions
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.

27. Balancing Redox Reactions
SECTION19.2
Balancing Redox Reactions
Balancing Redox Equations Using Half-Reactions (cont.)
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.

28. Balancing Redox Reactions
SECTION19.2
Balancing Redox Reactions
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.

29. Balancing Redox Reactions
SECTION19.2
Balancing Redox Reactions
Balancing Redox Equations Using Half-Reactions (cont.)

30. A redox reaction can be split into two parts called ____.
SECTION19.2
Section Check
A redox reaction can be split into two parts called ____.
A. net reactions
B. oxidation-reactions
C. half-reactions
D. reduction-reactions

31. SECTION19.2
Section Check
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

33. Redox Reactions Chemistry Online Study Guide Chapter Assessment
Resources
Chemistry Online
Study Guide
Chapter Assessment
Standardized Test Practice

34. Oxidation and Reduction
SECTION19.1
Oxidation and Reduction
Study Guide
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.

35. Oxidation and Reduction
SECTION19.1
Oxidation and Reduction
Study Guide
Key Concepts

36. Balancing Redox Reactions
SECTION19.2
Balancing Redox Reactions
Study Guide
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.

37. Balancing Redox Reactions
SECTION19.2
Balancing Redox Reactions
Study Guide
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.

38. CHAPTER19
Redox Reactions
Chapter Assessment
What type of reaction involves the transfer of electrons from one atom to another?
A. synthesis
B. decomposition
C. double replacement
D. redox

39. CHAPTER19
Redox Reactions
Chapter Assessment
Less electronegative atoms in redox reactions are most often ____.
A. oxidized
B. reduced
C. oxidizing agents
D. neutral

40. CHAPTER19
Redox Reactions
Chapter Assessment
Any chemical unit involved in a process is called a(n) ____.
A. atom
B. type
C. species
D. ion

41. Redox Reactions Determine the oxidation number of oxygen in HNO3.
CHAPTER19
Redox Reactions
Chapter Assessment
Determine the oxidation number of oxygen in HNO3.
A. +3
B. –3
C. +2
D. –2

42. Redox Reactions Determine the oxidation number of nitrogen in HNO3.
CHAPTER19
Redox Reactions
Chapter Assessment
Determine the oxidation number of nitrogen in HNO3.
A. +1
B. +4
C. +5
D. –5

43. CHAPTER19
Redox Reactions
Standardized Test Practice
In the reaction MgI2 + Br2 → MgBr2 + I2, what is the oxidation number of I2?
A. –1
B. +1
C. 0
D. +½

44. Redox Reactions Which is NOT an oxidizing agent in a redox reaction?
CHAPTER19
Redox Reactions
Standardized Test Practice
Which is NOT an oxidizing agent in a redox reaction?
A. substance reduced
B. electron acceptor
C. oxidizer of another substance
D. electron donor

45. CHAPTER19
Redox Reactions
Standardized Test Practice
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

46. CHAPTER19
Redox Reactions
Standardized Test Practice
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

47. Redox Reactions What is the oxidizing agent in the following equation?
CHAPTER19
Redox Reactions
Standardized Test Practice
What is the oxidizing agent in the following equation?
Na2SO4 + 4C → Na2S + 4CO
A. C
B. S
C. O
D. Na

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