physical chemistry topic included electrochemistry

1. Dr. Khadija Munawar
Assistant Professor
Department of Chemistry, School of Natural Sciences,
National University of Sciences and Technology(NUST), Islamabad
Course Code: CH-380
Course Title: Physical Chemistry-I
BS-Chemistry ( Semester V)

2. Electrochemistry
Lecture#11
24th October, 2023

3. An Introduction to Electrochemistry
Branch of science which deals with the study of
all physical and chemical processes which can be
carried out by electrical energy and the processes
which proceed with the generation of electricity.
Electrochemistry is concerned with the
conversion of electrical energy into chemical
energy in electrolytic cells as well as the
conversion of chemical energy into electrical
energy in galvanic or voltaic cells.

4. An Introduction to Electrochemistry
Electrochemical cell:
An electrochemical cell is a device that can
produce electrical work in the surroundings.
For example, the commercial dry cell is a sealed cylinder with
two brass connecting terminals protruding from it. One
terminal is stamped with a plus sign and the other with a
minus sign. If the two terminals are connected to a small
motor, electrons flow through the motor from the negative to
the positive terminal of the cell. Work is produced in the
surroundings and a chemical reaction, the cell reaction,
occurs within the cell.

5. An Introduction to Electrochemistry
Electrochemical cell: Two types
1. In an electrolytic cell, a process called electrolysis
takes place. In this process, electricity is passed
through a solution or the fused state of electrolyte.
The electricity provides sufficient energy to cause
an otherwise non-spontaneous oxidation-
reduction reaction to takes place.
2. In a galvanic cell/voltaic cell, electricity is
produced results from a spontaneous oxidation-
reduction reaction taking place in a solution.

6. An Introduction to Electrochemistry
Electrochemical cell:
Components:
An electrochemical cell consists of two electrodes, or
metallic conductors, in contact with an electrolyte, an
ionic conductor. An electrode and its electrolyte comprise
an electrode compartment. The two electrodes may
share the same compartment. If the electrolytes are
different, the two compartments may be joined by a salt
bridge, which is a tube containing a concentrated
electrolyte solution (for instance, potassium chloride in
agar jelly) that completes the electrical circuit and
enables the cell to function.

7. An Introduction to Electrochemistry
Electrochemical cell:
1. Electrolytic cell
The process of electrolysis is
carried in an apparatus called
the Electrolytic cell. The cell
contains water-solution of an
electrolyte in which two
metallic rods (electrodes) are
dipped. These rods are
connected to the two terminals
of a battery (source of
electricity). The electrode
connected to the positive
terminal of the battery attracts
the negative ions (anions) and is
called anode. The other
electrode connected to the
negative end of the battery
attracts the positive ions
(cations) and is called cathode.

8. An Introduction to Electrochemistry
Electrochemical cell:
1. Electrolytic cell

9. An Introduction to Electrochemistry
Electrochemical cell:
1. Electrolytic cell
Examples:
Down’s cell: Extraction of sodium by the
electrolysis of fused sodium chloride is
carried out.
Nelson’s cell: Caustic soda (NaOH) is
obtained by the electrolysis of
concentrated aqueous solution of
sodium chloride.

10. Electrochemistry
Lecture#12
27th October, 2023

11. Electrochemical cell: Two types

12. An Introduction to Electrochemistry
Electrochemical cell:
2. Galvanic/Voltaic cell
When a spontaneous reaction
takes place in a galvanic cell,
electrons are deposited in one
electrode (the site of oxidation,
the anode) and collected from
another (the site of reduction,
the cathode), and so there is a
net flow of current which can
be used to do work.
Note that the + sign of the
cathode can be interpreted as
indicating the electrode at
which electrons enter the cell,
and the – sign of the anode is
where the electrons leave the
cell.

13. An Introduction to Electrochemistry
Electrochemical cell:
2. Galvanic/Voltaic cell
In a galvanic cell,
the cathode has a higher
potential than the
anode: the species undergoing
reduction, withdraws electrons
from its electrode (the
cathode), so leaving a relative
positive charge on it
(corresponding to a high
potential).
At the anode, oxidation results
in the transfer of electrons to
the electrode, so giving it a
relative negative charge
(corresponding to a low
potential).

14. An Introduction to Electrochemistry
Electrochemical cell:
2. Galvanic/Voltaic cell: Daniel Cell
One version of the Daniell cell.
The copper electrode is the cathode and the zinc electrode is
the anode. Electrons leave the cell from the zinc electrode
and enter it again through the copper electrode.

15. Activity
Compare electrolytic and galvanic
cell in terms of similarities and
dissimilarities

16. The reducing agent (or reductant) is the electron donor;
The oxidizing agent (or oxidant) is the electron acceptor;
Any redox reaction may be expressed as the half-reactions.
As the reaction proceeds, the electrons released in the oxidation
Red1→ Ox1+ νe− at one electrode travel through the external circuit and
re-enter the cell through the other electrode. There they bring about
reduction Ox2+ νe− → Red2.
The reduced and oxidized species in a half-reaction form a redox
couple. In general we write a couple as Ox/Red and the corresponding
reduction half-reaction as Ox+ νe− → Red
For example
In the ‘Daniell cell’, the redox couple at one electrode is Cu2+/Cu and at
the other is Zn2+/Zn

17. Cell notation:
Explanation and examples will be discussed in class on board