(1) Electrochemistry involves the transfer of electrons during chemical reactions and electrical changes brought about by chemical changes. (2) Cell potential, measured in Volts, is the tendency of a species to lose or gain electrons compared to the Standard Hydrogen Electrode potential of 0.00V. (3) The Standard Hydrogen Electrode consists of hydrogen gas bubbling over a platinum electrode in a solution of 1M hydrogen ions, and its reduction potential is defined as 0.00V.

1. (1) Review the concept of “Oxidation”
and “Reduction.”
(2)Define the term “cell potential.”
(3)Illustrate the Standard Hydrogen
Electrode (SHE) and Standard
Electrode (reduction) potentials.
1

2. What is Electrochemistry?
 Electrochemistry is the study of chemical reactions
and their associated electrical changes.
 It is also looks at chemical changes that an electrical
current can bring about.
2

3. Transfer of electrons
 Electrochemistry involves the transfer of electrons.
3

4. Cell Potential
 If a strip of metal (electrode) is placed in a solution of its
ions, the metal loses electrons to form its cation.
M(s) → Mn+
(aq) + n e-
 The cations in solution may accept some of the lost
electrons and get reduced to the metal atoms.
Mn+
(aq) + n e- → M(s)
 At equilibrium, the charge difference that develops
between the metal strip and the solution is called a
potential difference.
4

5. Half Cell
5

6. Relative Cell Potential
 More reactive metals lose electrons with greater ease
and so the equilibrium position of the redox reaction
below lies more to the left.
Mn+
(aq) + n e- ⇌ M(s)
 More reactive metals therefore possess more negative
reduction potentials and less reactive metals will
possess more positive reduction potential differences.
6

7. Cell-Potential
 Cell potential (measured in Volts and sometimes
known as the electromotive force, emf) is the
tendency of species to lose or gain electrons.
 E° represents the standard electrode potential,
which is the potential of a species compared with
the potential of a Standard Hydrogen Electrode.
2H+ + 2e- ↔ H2 E°
cell = 0.00V 7

8. Standard Hydrogen Electrode
The Standard Hydrogen Electrode (S.H.E.) consists of
Hydrogen gas at 298K and 1 atm bubbling over a platinum
electrode immersed in a solution of H+ ions with
concentration 1 moldm-3.
2H+
(aq) + 2e- ⇌ H2 (g, 1 atm) Eᶿ = 0.00 V 8

9. Standard cell potential of Zn
half cell
 Zn (aq) ⇌ Zn2+
(aq) + 2e- Eᶿ = + 0.76 V
 Zn2+
(aq) + 2e- ⇌ Zn (s) Eᶿ = - 0.76 V
9

10. Cell-Potential
 For species with a positive value, they have
a tendency to be reduced.
 They are strong oxidizing agents.
 They are usually non-metals.
 For species with a negative value, they have
a tendency to be oxidized.
 They are strong reducing agents.
 They are usually metals.
10

11. Table of standard reduction potentials
11

12. Cell-Potential
 The total cell-potential can be expressed as follows:
E°
cell = E°
ox. + E°
red.
 E.g.:
Zn(s) + Cu2+
(aq) ↔ Zn2+
(aq) + Cu(s)
 E°
Zn2+(aq)+ 2e-⇌Zn (s) = -0.76V
 E°
Cu2+(aq) + 2e-⇌ Cu (s) = +0.34V
 Thus:
E°
cell = (0.76 + 0.34)V
= 1.10V
12