Introduction Of Electrochemistry Video Lecture | Additional Study Material for Class 12

electrochemistry introduction
electrochemistry is the study of
production of electricity from energy
released during spontaneous chemical
reactions and the use of electrical
energy to bring about non spontaneous
chemical transformations batteries and
fuel cells convert chemical energy into
electrical energy and are used on a
large scale in various instruments and
devices the reactions carried out
electrochemically can be energy
efficient and less polluting
electrochemical cells if an external
opposite potential is applied in the
galvanic cell and increased slowly we
find that the reaction continues to take
place till the opposing voltage reaches
the value 1.1 volt when the reaction
stops altogether and no current flows
through the cell any further increase in
the external potential again starts the
reaction but in the opposite direction
it now functions as an electrolytic cell
a device for using electrical energy to
carry non-spontaneous chemical reactions
Daniell cell in a Daniell cell the redox
reactions shown above
takes place this reaction is a
combination of two half-reactions
whose addition gives the overall cell
reaction these reactions occur in two
different portions of the Daniell cell
the reduction half reaction occurs on
the copper electrode while the oxidation
half-reaction
occurs on the zinc electrode these two
portions of the cell are also called
half cells or redox couples the copper
electrode may be called the reduction
half cell and the zinc electrode the
oxidation half cell
Nernst equation Nernst showed that for
the electrode reaction shown above the
electrode potential at any concentration
measured with respect to standard
hydrogen electrode can be represented
but concentration of solids M is taken
as unity and we have in Daniel cell they
electrode potential for any given
concentration of C U to the power of 2
positive and is at yin to the power of 2
positive ions it can be seen that a cell
depends on the concentration of both see
you to the power of 2 positive and is at
the N to the power of 2 positive ions it
increases with increase in the
concentration of CO 2 positive ions and
decrease in the concentration of easy DN
2 positive ions by converting the
natural logarithm in equation to the
base 10 and substituting the values of
our F and T is equal to 298 K it reduces
to the form equilibrium constant if the
circuit in Daniell cell is closed then
we note that the reaction shown above
takes place and as time passes the
concentration of is at the end to
positive keeps on increasing while the
concentration of Cu to positive keeps on
decreasing at the same time voltage of
the cell as read on the voltmeter keeps
on decreasing after some time we shall
note that there is no change in the
concentration of Cu to positive and is
that n to positive ions and at the same
time voltmeter gives zero reading this
indicates that equilibrium has been
attained in this situation the Nernst
equation may be written
measurement of the conductivity of ionic
solution to platinum electrodes coated
with platinum black finely divided
metallic platinum is deposited on the
electrodes electrochemically these have
area of cross-section equal to a and are
separated by distance L therefore
solution confined between these
electrodes is a column of length L and
an area of cross section a the
resistance of such a column of solution
is then given by the above equation
molar conductivity molar conductivity is
defined as the conductivity of an
electrolyte solution divided by the
molar concentration of the electrolyte
and so measures the efficiency with
which a given electrolyte conducts
electricity in solution it's units are
Siemens per meter per molarity or
Siemens meter squared per mole
the usual symbol is a capital lambda
Faraday's law of electrolysis first law
the amount of chemical reaction which
occurs at any electrode during
electrolysis by a current is
proportional to the quantity of
electricity passed through the
electrolyte second law the amounts of
different substances liberated by the
same quantity of electricity passing
through the electrolytic solution are
proportional to their chemical
equivalent Wade's primary batteries in
the primary batteries the reaction
occurs only once and after use over a
period of time battery becomes dead and
cannot be reused again the most familiar
example of this type is the dry cell the
cell consists of a zinc container that
also access anode and the cathode is a
carbon rod surrounded by powered
manganese dioxide and carbon the space
between the electrodes is filled by a
moist paste of ammonium chloride and
zinc chloride the electrode reactions
are complex but they can be written
approximately as follows secondary
batteries a secondary cell can be
recharged by passing current through
in the opposite direction so that it can
be used again the most important
secondary cell is the lead storage
battery commonly used in automobiles and
inverters it consists of a lead a note
and a grid of LED packed with LED
dioxide as cathode
on charging the battery the reaction is
reversed and pbso4 s on anode and
cathode is converted into PB and PB o 2
respectively fuel cells one of the most
successful fuel cells uses the reaction
of hydrogen with oxygen to form water
the cell was used for providing
electrical power in the Apollo space
program the water vapors produced during
the reaction were condensed and added to
the drinking water supply for the
astronauts in the cell hydrogen and
oxygen are bubbled through porous carbon
electrodes into concentrated aqueous
sodium hydroxide solution catalysts like
finely divided platinum or palladium
metal are incorporated into the
electrodes for increasing the rate of
electrode reactions corrosion in
corrosion a metal is oxidized by loss of
electrons to oxygen and formation of
oxides corrosion of iron occurs in
presence of water and air at a
particular spot figure of an object made
of iron oxidation takes place and that
spot behaves as anode and we can write
the reaction as shown electrons released
at anodic spot move through the metal
and go to another spot on the metal and
reduce oxygen in presence of H+ this
spot behaves as cathode with the
reaction the hydrogen economy carbon
dioxide produced by the combustion of
fossil fuels results in the greenhouse
effect this is leading to a rise in the
temperature of the Earth's surface
causing polar ice to melt and ocean
levels to rise this will flood low-lying
areas along the curve
and some island nations such as Maldives
face total submergence in order to avoid
such a catastrophe we need to limit our
use of carbonaceous fuels hydrogen
provides an ideal alternative as its
combustion drizzles
in water only therefore hydrogen can be
used as a renewable and non polluting
source of energy this is the vision of
hydrogen economy