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Electrochemistry | Electrochemical Cells#

Electrochemical Cells#

Devices which can convert electrical energy into chemical energy or chemical energy into electrical energy are called electrochemical cells.
There are two types of electrochemical cells: (a) Electrolytic cell (b) Galvanic cell.

Electrolytic Cell#

An electrolytic cell converts electrical energy into chemical energy.
In an electrolytic cell, the reaction is non-spontaneous. So, \(ΔG > 0\). The reaction is made spontaneous by supplying current.
Anode is positively charged and cathode is negatively charged.

Galvanic Cell#

It is also known as Daniell Cell.
A galvanic cell converts chemical energy into electrical energy.
Current is flown by a spontaneous process. So, \(ΔG < 0\).
Anode is negative and cathode is positive in a galvanic cell.
Oxidation Half Cell Reaction (At anode):

\[Zn_{(s)} → Zn^{+2}_{(aq)} + 2e^-\]

Reduction Half Cell Reaction (At cathode):

\[Cu^{+2}_{(aq)} + 2e^- → Cu_{(s)}\]

Current flows from cathode to anode in an external circuit.

Salt Bridge#

It is a U-Shaped tube which is filled with a mixture of agar-agar and an inert electrolyte like KNO₃, NaNO₃, KCl etc and both the ends of this tube are sealed with cotton wool.

Functions of Salt Bridge:#

It completes the inner circuit.
It prevents the diffusion of electrolytic solution in the two half cells.
It maintains electrical neutrality in the two cells. If excess electrons get accumulated, then salt bridge releases cations like Na⁺ to maintain electrical neutrality. If excess electrons are consumed, then salt bridge releases anions like Cl^- and NO₃^- to maintain electrical neutrality.

Characteristics of Inert Electrolyte:#

Both of its ions should not participate in the cell reactions.
Velocities of both ions of the electrolyte should be same. In the above figure, velocity of Na⁺ is approximately equal to velocity of NO₃^-.