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Galvanic Cell

Chemistry

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Working of electrochemical cell

An electrochemical cell consists of two half-cells. Each half-cell consists of an electrode and an electrolyte.The two half-cells may use the same electrolyte, or they may use different electrolytes. The chemical reactions in the cell may involve the electrolyte, the electrodes, or an external substance.

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Half-cells or redox cells

A half-cell is a structure that contains a conductive electrode and a surrounding conductive electrolyte separated by a naturally occurring Helmholtz double layer.

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Salt bridge

1. It provides an electrical contact between the two solutions and thereby completes the electrical circuit.
2. It prevents the mixing of electrode solutions. Maintains electrical neutrality in both the solution by a flow of ions.

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Electrochemical reaction between zink and copper

This is the chemical reaction between zinc and copper sulphate.

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Electrochemical cell reaction between copper and silver nitrate

Silver nitrate is soluble in water. Its aqueous solution contains Ag(aq) and NO(aq) ions. Similarly an aqueous solution of copper(II) nitrate contains Cu(aq) and NO(aq) ions.
We can rewrite the chemical equation in the following form

(s) + (aq) + (aq)   Cu(aq) + (aq) + (s)

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Representation for electrochemical cell

This is the representation for electrochemical cell of copper sulphate and zinc sulphate solution.

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Method to write cell reactions

  • A double vertical line (||) is used to separate the anode half reaction from the cathode half reaction. This represents the salt bridge. 
  • The anode (where oxidation occurs) is placed on the left side of the ||. The cathode (where reduction occurs) is placed on the right side of the ||. 
  • A single vertical line (|) is used to separate different states of matter on the same side, and a comma is used to separate like states of matter on the same side

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Standard EMF of a Cell

The electromotive force (EMF) is the maximum potential difference between two electrodes of a galvanic or voltaic cell. The standard EMF of a cell is defined as the EMF of a cell measured under standard conditions. Standard conditions are as following:
1. The temperature at which potential is measured should be .
2. The concentration of the electrolyte should be 1M.
3. If the electrode is gaseous, pressure should be 1 atm.
4. All the species used should be pure.
To consider the EMF of a cell as a standard EMF of a cell, all four conditions should be met.
It is denoted by the symbol .
Hence we can write standard EMF of a cell as,

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Features of electrochemical cell

An electrochemical cell is a device that can generate electrical energy from the chemical reactions occurring in it, or use the electrical energy supplied to it to facilitate chemical reactions in it.
It is of two types:
1. Electrolytic cell
2. Galvanic cell