COMMERCIAL
CELLS
What are Commercial Cells?
Commercial cells are the source of energy. They are electrochemical
devices that are used as a source of energy, and they provide a relatively constant voltage
over time. Batteries are formed when two or more commercial cells are connected in series.
These batteries are used to produce portable electrical energy. Thus, a battery is an
electrochemical cell arrangement used as a source of electrical power.
The following criteria should be included in a useful battery:
It should be light and compact so that it can be easily transported.
It should have long life both when it is used and when it is not used.
The voltage or potential of the battery should not vary appreciably during its use.
Commercial batteries are galvanic cells that use solids or pastes as reactants to
maximize the electrical output per unit mass.
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An electrochemical cell is a device in which a redox reaction (chemical reaction)
is utilized to get electrical energy commonly referred to as voltaic or galvanic cell
The electrode where oxidation occurs is called anode while the electrode where reduction
occurs is called cathode
An example for Electrochemical cell or galvanic cell - Daniel Cell
Zinc Electrode dipped in ZnSO4, solution
Oxidation
Copper Electrode dipped in CuSO4, solution
Reduction
Each electrode is referred to as half-cell which are connected through a salt bridge.
Electrode Reaction:
At Anode Zn Zn2+ + 2e-
At Cathode Cu2+ +2e- Cu
Electrolytic cell:
A device in which the electrical energy is converted to chemical energy and
resulting in a chemical reaction. An electrolytic cell is one kind of battery that requires an
outside electrical source to drive the non-spontaneous redox reaction. Rechargeable
batteries act as electrolytic cells when they are being recharged.
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Batteries use a chemical reaction to do work on charge and produce a voltage between
their output terminals.
The basic element in a battery is called electrochemical cell and makes use of an
oxidation/reduction reaction.
An electrochemical cell which produces an external current is called a voltaic cell.
Voltages generated by such cells have historically been referred to as E.M.F
(Electromotive Force).
EMF is the maximum potential difference between two electrodes of a
galvanic or voltaic cell
Batteries are devices where several electrochemical systems are connected together
in series.
Can store chemical energy for later release as electricity
It is a source of direct electric current at a constant voltage
Types of Batteries:
Primary battery (Primary cells):
The cell reaction is not reversible. When all the reactants have
been converted to product, no more electricity is produced and the battery is dead.
Secondary battery (secondary cells):
The cell reactions can be reversed by passing electric current
in the opposite direction. Thus, it can be used for a large number of cycles.
Flow battery and fuel cell:
The materials (reactants, products, electrolytes) pass
through the battery, which is simply an electrochemical cell that converts
chemical to electrical energy.
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Types of Primary Batteries:
Dry or Leclanche cell
Alkaline battery
Lithium batteries
Dry or Leclanche cell:
he most familiar commercial cells are dry cells. These are used in
torches, toys, calculators, tape recorders, and many other devices. The dry cell consists of
a Zn cylinder which is filled with a paste of NH4Cl and ZnCl2. The zinc cylinder act as an
anode and the carbon rod is surrounded by a black paste of MnO2 and carbon powder acts
as a cathode. When the cell is working, Zinc loses e- and produced Zn+2 ion which is
dissolved in the electrolyte. The electrons pass around the external circuit and are taken up
at the cathode. This causes the discharge of NH4+ ion from the electrolyte.
Anodic Reaction:
Zn(s) Zn²+(aq) + 2e-
Cathodic reaction:
2NH(aq) + 2MnO2(s) + 2e- Mn2O3(s) + H2O(l)+2NH3
Some of the complexity of this reaction comes from the fact that
the reduction of the ammonium ion produces two gaseous products.
2NH4+(aq) + 2e- 2NH+H₂ (g)
Which must be absorbed to prevent the build-up of gas pressure
ZnCl2 (aq) + 2NH3 (g) Zn(NH3)2Cl₂ (s)
2MnO2 (s) + H2(g) Mn2O3(s) + H2O(l)
Zn (s) + 2 MnO2(s) + 2 NH4CL (aq) ZnCL2+ Mn2O3(s) + 2NH3+ H₂O
