Question

Can an electrochemical cell act as an electrolytic cell? How? Explain the construction and working of a standard hydrogen electrode. What is an electrochemical series? How does it predict the feasibility of a certain redox reaction? Give some uses of electrochemical cells. How is standard electrode potential of a cell related to equilibrium constant and Gibbs free energy change?

Answer 1

To answer this question you must recall the properties and formation of electrochemical cells. In an electrochemical cell, the chemical energy of a spontaneous redox reaction is converted into electrical energy and in an electrolytic cell, electrical energy is used to carry out a non-spontaneous redox reaction.

Complete step by step answer:
Yes, an electrochemical cell can act as an electrolytic cell if a potential difference greater than the potential of the electrochemical cell is applied. In this case, the reaction begins to proceed in the opposite direction, that is, the non-spontaneous reaction takes place like in an electrolytic cell.The standard hydrogen electrode consists of a platinum electrode coated with platinum black. The electrode is then dipped in an acidic solution and pure hydrogen gas is bubbled through it. The concentration of hydrogen ions in the solution is maintained at one molar and the pressure of the hydrogen gas is maintained at one bar. The electrode can act as either a cathode or as an anode depending on the connection of the other half cell. When the two half cells are connected to form a complete cell, it gives the reduction potential of the other half cell.
The electrochemical series is a list of the increasing order of reduction potentials of different electrodes. The species present higher is a stronger reducing agent and the species present lower in the series is a better oxidizing agent. A certain redox reaction is possible only if the species having a higher reduction potential is reduced.
Electrochemical cells are used as batteries. One common example is a $1.5$ volt cell which is used in appliances like clocks and remotes.
The relation between electrode potential and Gibbs free energy is given as:
${{\Delta }}{{\text{G}}^o} = - {\text{nF}}{{\text{E}}_{{\text{cell}}}}$
The relation between electrode potential and equilibrium constant is given as:
${{\text{E}}_{{\text{cell}}}} = \dfrac{{{\text{RT}}}}{{{\text{nF}}}}{\text{lnK}}$

Note:
Electrolysis is the breaking down of an electrolyte due to the supply of electricity. In electrolysis we need to supply external energy to initiate chemical reaction which is non spontaneous in nature otherwise. The second law of Faraday states that when the same amount of energy is passed through the electrolytic solution of a number of substances then and the equivalent weight of electrolyte in each solution will be in a ratio to each other.