What are electrochemical cells? Name the two types of electrochemical cells.

Explanation

In this device the Gibbs energy of the spontaneous redox reaction is converted into electrical work which may be used for running a motor or orther electrical gadgets like heater, fan, geyser etc.

Working of electrochemical cell : Let us explain the working of electrochemical cell with the help of following redox reaction: `Zn(s)+Cu^(2+)(aq)rarrZn^(2+)(aq)+Cu(s)`
The cell consists of two beakers. One beaker contains 1 M solution of `CuSO_(4)`. The other beaker contains 1 M solution of `ZnSO_(4)`. A zinc rod is dipped in `ZnSO_(4)` solution. A copper rod is dipped in `CuSO_(4)` solution. These metallic rods are known as electrodes. These are connected with the help of connecting wire through a key. Ammeter is used to known the flow of electric current. The solutions in two beakers are connected by an inverted U-tube, which contains saturated solution of inert electrolyte such as KCl, `KNO_(3)` etc, and known as salt bridge. The electolyte does not undergo any chemical change. The two openings of the tube are plugged with some porous material such as glass wool or cotton.
When the circuit is completed by inserting the key, then electric current flows through the circuit.
Following observations are made :
i) Zinc rod gradually loses its weight.
ii) The concentration of `Zn^(2+)` ions in `ZnSO_(4)` solution increases.
iii) Copper gets collected at the copper electrode.
iv) The concentration of `Cu^(2+)` ions in `CuSO_(4)` solution decreases.
There is a flow of electrons in the external circuit from zinc rod to copper rod. Therefore, electric current flows from Cu to Zn rod.