Electrochemistry

A device that converts electrical energy to chemical energy and vice versa is said to be an electrochemical cell. The reactions can be of two types, namely spontaneous and non-spontaneous chemical reactions. Spontaneous chemical reactions are the ones that take place on their own without the aid of any external current or potential difference. In contrast, non-spontaneous chemical reactions take place with the aid of the external power supply. In other words, in the case of spontaneous reactions, the energy possessed by the molecules is equal to its activation energy.

In contrast, the reverse is true for the non-spontaneous reaction, i.e. the energy possessed by the molecules is not equal to the activation energy. In a spontaneous chemical reaction process, Gibb’s free energy of the system decreases. Electrochemical cells are of two types. They are namely galvanic cells and electrolytic cells.

Galvanic cells:

The cell that converts chemical energy into electrical energy through the redox reaction is referred to as a galvanic cell. The oxidation and reduction reaction takes place in two different compartments containing two different electrodes and a suitable electrolyte that supports the mobility of the electrons and the flow of electric currents through them. The major components of galvanic cells are salt bridge, electrodes, electrolytes, cell potential. A Salt bridge is an inverted U-shaped tube with concentrated inert electrolytes that helps to maintain the charge density across the two compartments. Each compartment contains an electrode and electrolyte, said as half cells named as anode and cathode. Electrode potential is the potential difference that drives the current in the opposite direction to carry out the oxidation and reduction. The voltage at which electrolysis is thermodynamically preferred is the difference in the cathode and anode’s electrode potentials, calculated by the Nernst equation. Theoretically, this helps in the calculation of the cell potential and the electrode potential of both anode and cathode. Moreover, this also helps to predict whether the cell reaction is feasible or not.

Example of Galvanic cell:

Daniel cell is a galvanic cell having zinc and copper as two half cells.

Electrochemical Series:

The arrangements of different elements in order of their increasing electrode potential with reference to the standard hydrogen electrode results in the electrochemical series. The various electrode potential is measured against the hydrogen electrode, whose value is equal to zero.

Electrolytic cell:

A device that converts electrical energy into chemical energy is referred to as an electrolytic cell. The working principle of this cell is just the opposite of galvanic cells. In this case, the redox reaction takes place in the same compartment as both the electrodes are dipped in the same container containing the electrolytes. The electrodes are connected to an external power source supply that completes the circuit. When the current flows, the Cations and anions start moving towards the opposite polarity, and oxidation and reduction reactions simultaneously occur in cathode and anode, respectively.

Example:

Electrolysis of molten salt is an example of an electrolytic cell.

Conclusion:

The branch of chemistry deals with the study of relationships between electrical energy and chemical changes. The chemical reactions involving the generation or input of electric currents are referred to as electrochemical reactions. The cell that converts chemical energy into electrical energy through the redox reaction is a galvanic cell, and a device that converts electrical energy into chemical energy is an electrolytic cell. The reactions can be of two types, namely spontaneous and non-spontaneous chemical reactions. Spontaneous chemical reactions are the ones that take place on their own without the aid of any external current or potential difference.

In contrast, non-spontaneous chemical reactions take place with the aid of the external power supply. In other words, in the case of spontaneous reactions, the energy possessed by the molecules is equal to its activation energy. In contrast, the reverse is true for the non-spontaneous reaction, i.e. the energy possessed by the molecules is not equal to the activation energy. The arrangement of different elements in order of their increasing electrode potential with reference to the standard hydrogen electrode results in an electrochemical series. The various electrode potential is measured against the hydrogen electrode, whose value equals zero.