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Lecture Notes
Electrochemistry
AP Chemistry
I. Introduction of terms
A. ElectrochemistryB. currentC. conductor1. metallic conductor 2. electrolytic conductor-
II. Voltaic Cells
A. DefinitionB. This type of cell is _____________________.
C. Consists of
D. In this type of electrochemical cell, oxidation takes place at the ________
while reduction takes place at the ___________.
E. Illustration:
cell reaction-
salt bridge-
III. Notation for Voltaic Cells
A. anode || cathode
B. In order of reactants and products
C. | = phase boundary
D. Examples:
E. When the metal ion is NOT the electrode the electrode must be included.
Example:
IV. Electromotive Force (EMF)
A. DefinitionB. Maximum work obtained equation:
C. Examples:
1. Example 19.3
2. Exercise 19.4
V. Standard Cell emf’s and Standard Electrode Potentials
A. A cell emf is a measure
B. The cell emf is composed of a contribution from the anode and the
cathode.
1. oxidation potential2. reduction potentialC. Table 19.1 lists the Standard Reduction Potentials for substances in
aqueous solution.
D. Calculating overall cell potential
1. Equation:
2. Turning a reduction potential into an oxidation potential
a.
b.
3. For a given cell:
a. Determine the reduction half reaction and find the reduction
potential.
b. The other half cell is then reversed, both the equation and the
sign on the potential number.
c. Balance the half cells to obtain the cell reaction.
d. The half cell potentails are added algebraically to obtain the
cell potential.
4. Spontaneity
a. If the Ecell is ______________ then the reaction is __________________.
b. If the Ecell is _______________ the reaction is ____________________.
5. Examples:
a. Al(s)|Al3+ || Fe2+(aq)|Fe(s)
b. Zn(s)|Zn2+(aq) || Ag+(aq)|Ag(s)
c. Does the following reaction occur spontaneously?
Zn2+(aq) + 2 Fe2+(aq) ---> Zn (s) + 2 Fe3+(aq)
d. Does this reaction occur spontaneously?
Zn(s) + Fe2+(aq) ---> Zn2+ (aq) + Fe(s)
E. Strengths of Oxidizing and Reducing Agents
1. Oxidizing Agents
2. Reducting Agents
3. Examples: Give in order of increasing oxidizing strength: Cl2 (aq),
H2O2 (aq), Fe3+(aq)
In order of increasing reducing strength: H2 (g), Al (s), Cu (s)
VI. Electrolytic Cells
A. Definition: An electrochemical cell
B. electrolysis1. Electrolysis of MOLTEN Salts (Down’s Cell)
a. Example: Exercise 19.14
2. Aqueous Electrolysis
a. Aqueous or with water: the half reactions of water
b. Chloride Solutions
c. Sulfuric acid solutions
3. Examples:
*NOTE: It is difficult to reduce
VII. Stoichiometry of Electrolysis
A. Electrical Units
1. ampere2. coulomb3. faradayB. Example problems:
1. How many grams of zinc ions will be reduced by 1.00 mole of
electrons?
2. How many grams of Zn with be plated out by 0.200F of electricity?
3. How many grams of Al will be plated out by a current of 3.00 amps
flowing through the cell for 2.00 hours?
4. Exercise 19.16
5. Exercise 19.17
The Nernst Equation is used to:
1.
2.
3.
E = cell potential under nonstandard conditions
E˚ = standard cell potential
n = number of moles transferred in the redox or cell half reaction
Q = reactant quotient
The reaction quotient is a ratio of concentrations or pressures of products to those of reactants,
each raised to the power indicated by the coefficient in the balanced equation.
Example: Cd (s) + 2 H+ (aq)  Cd2+ (aq) + H2 (g)
As the the reactions proceeds the cell emf, Ecell, ______________________________. As the
concentrations of products ___________________ the concentrations of the reactants
____________________. When the cell emf goes to zero the reaction comes to
__________________________.
Example 19.10
Exercise 19.11