Electrochemistry.
Electrochemistry
is defined as the branch of chemistry which deals with the relationship between
chemical energy and electrical energy taking place in a redo reaction and inter
conversion of one form of energy into another. A cell or a battery converts chemical
energy into electrical energy which
can be used to operate various equipments. The reverse process is also possible in which we can
make non–spontaneous processes occur by supplying external energy in form of
electrical energy. These inter conversions are carried out in equipments called
“Electrochemical Cells”. Electrochemical Cells are of two types:
1. Galvanic Cells: Converts chemical energy into electrical
energy
2. Electrolytic Cells: Converts electrical energy into chemical
energy
Conductors
and Non Conductors
Substances
around us can be divided into two classes based on their ability of conduct
electricity:
Non-Conductors: Those substances which do not allow
electric current to pass through them are called non-conductors or insulators.
Example: - wood, plastic glass, rubber etc.
Conductors: Those substances which allow electric
current to flow through tem are called conductors. Examples: Copper, Iron,
Gold, Silver, Graphite, salt solution etc.
Conductors can further be divided into two
groups:Metallic Conductors: These conductors conduct electricity
or electric current by movement of electrons without undergoing any chemical
change during the process. These conduct electricity in both solid as well as
molten state. Example: All the metals and GraphiteElectrolytes: Those substances which conduct electricity only when they are
present in aqueous solution or in molten state and not in solid form are called
electrolytes. These conduct electricity by movement of ions in solutions. For a
substance to conduct electricity; it must either have free electrons or ions
which carry electricity with them. Electrolytes neither have free electrons nor
free ion in solid state although they are ionic compound. This is because the
oppositely charged ions are held together by strong electrostatic attraction
and are not free to move. But when they are dissolved in water, the two ions
split up and become free to move in solution and now they are free to conduct
electricity. Examples of electrolytes are: NaCl, KCl,etc
Strong Electrolytes are those electrolytes which
dissociate completely in aqueous solution to give constituent ions. For
example: Inorganic salts like NaCl, KCl, Strong Acid like HCl, H2SO4, Strong bases like NaOH, KOH etc.
Weak Electrolytes are those electrolytes which partially
dissociate in aqueous solution to give constituent ions. For example:
weak acid like CH3COOH and Weak bases like NH4 OH.
Electrochemical Cells
Electrochemical
cells are of two types-
Galvanic cells (also known as voltaic cell): It is a device, in which a redox reaction is
used to convert chemical energy into electrical energy, i.e., electricity can
be obtained with the help of oxidation and reduction reaction. The chemical
reaction responsible for production of electricity takes place in two separate
compartments. Each compartment consists of a suitable electrolyte solution and
a metallic conductor. The metallic conductor acts as an electrode. The
compartments containing the electrode and the solution of the electrolyte are
called half-cells. When the two compartments are connected by a salt bridge and electrodes are joined
by a wire through galvanometer the electricity begins to flow. This is the
simple form of voltaic cell.
Electrolytic cells: In
this type of cells electrical energy is used to carry out a non-spontaneous
reaction.
In
simple words, one can say that in galvanic cells, chemical energy is converted
into electrical energy, while in electrolytic cell electrical energy is
converted into chemical energy.