What is galvanic cell ? Discuss briefly with one example.

Explanation

The device in which electrical energy is produced from chemical reactions is called galvanic cell. The common galvanic cell is a Daniel cell. It consists of two beakers containing 10 M solution of `ZnSO_(4)`, and 1.0M solution of `CuSO_(4)`. A zinc rod is dipped into `ZnSO_(4)` solution and a copper rod is dipped into `CuSO_(4)` solution. These rods act as electrodes. The solution in the two beakers are connected by inverted U tube containing concentrated solution of some electrolyte such as `KCI, KNO_(3)` or `NH_(4)NO_(3)`. The two openings of the U tube are plugged with some porous material such as glass wool or cotton.

The U tube which connects the two glass beakers is called salt bridge.
Salt bridge completes the cell circuit and increases the life of the cell. The arrangement is shown in Fig. When the two electrodes are connected through a voltmeter, the flow of electric current through external circuit is indicated by the voltmeter. The cell formed is called galvanic or voltaic cell.
The potential difference is due to the contribution of two half cells. At zinc electrode, zinc is oxidised to `Zn^(2+)` ions which go into the solution. The electrons released at zinc electrode move towards the other electrode (copper) through the outer circuit. These are accepted by `Cu^(2+)` ions of `CuSO_(4)` solution which are reduced to copper. Thus, oxidation occurs at zinc electrode and it is called anode. Reduction occurs at copper electrode and it is called cathode. The reactions may be represented as :
At anode :
`Zn(s)toZn^(2+)(aq)+2e" "` (oxidation)
At cathode :
`Cu^(2+)(aq)+2etoCu(s)" "` (reduction)
The overall cell reaction is
`Zn(s)+Cu^(2+)(aq)toZn^(2+)(aq)+Cu(s)`
The reactions occurring at anode and cathode are also referred as oxidation half cell reaction and reduction half cell reaction. The cell may be represented as :
`Zn(s)|Zn^(2+)(aq)||Cu^(2+)(aq)|Cu(s)`
Anode (-) Cathode (+)