Fundamentals of
Electrochemistry
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Chemistry 1103 Electrochemistry, Lecture notes of Chemistry
Chemistry 1103 Electrochemistry
Typology: Lecture notes
2018/2019
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Fundamentals of
Electrochemistry
Electrochemistry SkillsElectrochemistry Skills
- (^) Understand how voltaic cells work.
- (^) Be able to calculate standard reduction
potentials for voltaic cells, given the chemical
reactions.
- (^) Be able to describe a voltaic cell using the line
notation and visa versa. Know which way
electrons flow and where the anode and cathode
are.
- (^) Know how to work with the Nernst Eq. to include
concentration dependencies and calculate
equilibirum constants
Electrochemical cells
Redox reactions involve the transfer of electrons
between two species. The flow of electrons is an
electrical current.
Redox reactions can therefore be used to generate
electrical current. This is the basis of batteries and
fuel cells.
Electrochemical cells
An electrochemical cell is a store of chemical
energy in a closed system.
All reactants and products are contained
within the casing of the cell.
LEORA GEROA
Why is it important to balance
REDOX reactions?
Review: Placing oxidation number
How to Assign Oxidation
Numbers: The Fundamental Rules
- The oxidation number of any pure element is
zero. Thus the oxidation number of H in H 2
is zero.
- The oxidation number of a monatomic ion is
equal to its charge. Thus the oxidation number of
Cl in the Cl
- ion is -1, that for Mg in the Mg
ion is
+2, and that for oxygen in O
2- ion is -2.
- •
How to Assign Oxidation
Numbers: The Fundamental Rules
- The oxidation number of H is +1 in most
compounds. Exceptions are H2 (where H = 0) and
the ionic hydrides, such as NaH (where H = -1).
- The oxidation number of oxygen (O) is -2 in
most compounds. Exceptions are O 2
(where O = 0)
and peroxides, such as H 2
O 2
or Na 2
O 2
, where O = -1.
Check your knowledge: Oxidation/
Reduction
Balancing Redox Reactions
(continued)
STEP 4a. In ACID: Balance H by Inserting H
+
,
as needed
STEP 4b. In BASE: Balance H by (i) inserting 1
H
2
O for each missing H & (ii) inserting same
no. of OH
-
on OTHER SIDE OF REACTION as
H
2
Os added in (i)
Example: Balancing Redox
Reactions
Complete and Balance the Following
Reaction:
CuS (s) + NO
3
-
(aq) Cu
2+
(aq) + SO
4
2-
(aq)
+ NO (g)
STEP1. Split into 2 Half-Reactions
a.1 CuS Cu
2+
+ SO
4
2- oxidation
b.1 NO
3
-
NO reduction
I. Balancing Redox Reactions
(continued)
STEP 3. Balance O by inserting H
2
O into
equations as necessary
a.3 CuS + 4H
2
O Cu
2+
+ SO
4
2-
b.3 NO
3
-
NO + 2H
2
O
I. Balancing Redox Reactions
(continued)
STEP 4. ACIDIC, so Balance H by inserting
H
+
as needed
a4. CuS + 4H
2
O Cu
2+
+ SO
4
2-
+ 8H
+
b4. NO
3
-
+ 4H
+
NO + 2H
2