Transcript 1/20/14 Chapter 19: redox reactions

CHEMISTRY
Matter and Change
Chapter 19: Redox Reactions
CHAPTER
19
Table Of Contents
Section 19.1 Oxidation and Reduction
Section 19.2 Balancing Redox Equations
Click a hyperlink to view the corresponding slides.
Exit
SECTION
19.1
Oxidation and Reduction
• Describe the processes
of oxidation and
reduction.
• 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.
spectator ion: an ion
that does not participate
in a reaction and is not
usually shown in an
ionic equation
SECTION
Oxidation and Reduction
19.1
oxidation-reduction reaction reduction
redox reaction
oxidizing agent
oxidation
reducing agent
Oxidation and reduction are
complementary—as an atom is oxidized,
another atom is reduced.
SECTION
19.1
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.
SECTION
19.1
Oxidation and Reduction
Electron Transfer and Redox
Reactions (cont.)
SECTION
19.1
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–
SECTION
19.1
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.
SECTION
19.1
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.
SECTION
19.1
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.
SECTION
19.1
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.
SECTION
19.1
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.
SECTION
19.1
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.
SECTION
19.1
Oxidation and Reduction
Redox and Electronegativity (cont.)
SECTION
19.1
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.
SECTION
19.1
Oxidation and Reduction
Determining Oxidation Numbers (cont.)
SECTION
19.1
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.
SECTION
19.1
Oxidation and Reduction
Oxidation Numbers in Redox
Reactions (cont.)
SECTION
19.1
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
SECTION
19.1
Section Check
In redox reactions, more electronegative
elements tend to:
A. be reduced
B. be reducing agents
C. lose electrons
D. not change
SECTION
19.2
Balancing Redox Reactions
• Relate changes in
oxidation number to the
transfer of electrons.
• Use changes in
oxidation number to
balance redox
equations.
• Balance net ionic redox
equations using the
oxidation-number
method.
net ionic equation: an
ionic equation that
includes only the
particles that participate
in the reaction
SECTION
19.2
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.
SECTION
19.2
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.
SECTION
19.2
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.
SECTION
19.2
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.
SECTION
19.2
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.
SECTION
19.2
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.
SECTION
Balancing Redox Reactions
Balancing Redox Equations Using
Half-Reactions (cont.)
19.2
SECTION
19.2
Section Check
A redox reaction can be split into two
parts called ____.
A. net reactions
B. oxidation-reactions
C. half-reactions
D. reduction-reactions
SECTION
19.2
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
CHAPTER
Redox Reactions
19
Resources
Chemistry Online
Study Guide
Chapter Assessment
Standardized Test Practice
SECTION
Oxidation and Reduction
19.1
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.
SECTION
Oxidation and Reduction
19.1
Study Guide
Key Concepts
SECTION
19.2
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.
SECTION
19.2
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.
CHAPTER
19
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
CHAPTER
19
Redox Reactions
Chapter Assessment
Less electronegative atoms in redox
reactions are most often ____.
A. oxidized
B. reduced
C. oxidizing agents
D. neutral
CHAPTER
19
Redox Reactions
Chapter Assessment
Any chemical unit involved in a process is
called a(n) ____.
A. atom
B. type
C. species
D. ion
CHAPTER
19
Redox Reactions
Chapter Assessment
Determine the oxidation number of
oxygen in HNO3.
A. +3
B. –3
C. +2
D. –2
CHAPTER
19
Redox Reactions
Chapter Assessment
Determine the oxidation number of
nitrogen in HNO3.
A. +1
B. +4
C. +5
D. –5
CHAPTER
19
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
CHAPTER
19
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
CHAPTER
19
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
CHAPTER
19
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
CHAPTER
19
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
END OF SLIDE SHOW