Electrochemical Series

An electrochemical series is a series of chemical elements arranged in the order of their standard electrode potential.

This is the hydrogen electrode,

H+(aq) + e– →← 1/2H2(g)

The electrode potential is considered to be zero. By definition, the electrode potential is the reduction potential. Elements that are more prone to losing electrons in solution than hydrogen are considered electropositive; those that gain electrons from solution are lower in the series than hydrogen and are called electronegative. The most active metal lithium is placed on the top, the most active nonmetal Fluorine is at the bottom. So, we found that lithium is the strongest reducing agent and fluorine is the strongest oxidant.

 What is an Electrochemical Series?

Electrochemical series are lists of metals in order of decreasing reactivity or ease of oxidation. The higher metals in the series, such as alkali metals and alkaline earth metals, are more reactive or more easily oxidised than the lower metals in the series. This basically means that they can react more easily to form compounds. Those metals at the top of the active sequence are called active metals. Metals at the bottom of this range, such as transition metals, are very stable and unlikely to form bonds. These metals, such as copper and gold, are used to make coins and jewellery and are known as “precious” metals because of their low reactivity. An electrochemical series is a series of chemical elements arranged in the order of their standard electrode potential. Electrode potential is defined as the potential of a cell with one electrode as the cathode and a standard hydrogen electrode (SHE) as the anode. At the cathode, reduction always occurs whereas oxidation always occurs at the anode.

Applications in Electrochemical Series

Calculation of EMF

Each and every electrochemical cell comprises two half-cells connected to each electrode. Each half-cell undergoes a reaction, one oxidation and the other reduction. Each reaction corresponds to a potential, namely oxidation potential and reduction potential. 

Cell EMF is the sum of the oxidative and reducing capacity of cells. It measures the spontaneity of the overall reaction in the cell. It is also a measure of work which a cell can do. The electrochemical sequence helps us measure the EMF cell by taking the standard electrode potential values of the half-cells and then adding them appropriately. 

Ecell0=Ered0– Eox0 ,

where Ered0 is the standard reduction potential of the reducing half-cell and Eox0 is the standard reduction potential of the oxidising half-cell.

Measuring the spontaneity of responses

The viability or spontaneity of redox reactions is directly related to the corresponding reactive EMF cells:

• If the cell EMF is positive, the response is spontaneous. 

• If the cell EMF is negative, the response is non-spontaneous.

Therefore, we can understand whether a redox reaction can proceed spontaneously by looking at the reactants and products. We write the equations for the reduction and oxidation half-reactions. We then add their standard electrode potentials appropriately according to the electrochemical series. 

The resulting cellular EMF tells us whether the response is spontaneous.

Gibbs Free Energy Estimation

Gibbs free energy (ΔGcell0) is another measure of the spontaneity of a reaction. It is related to the EMF unit (E unit) as follows.

ΔGcell0=−nFEcell0,

where n is the number of electrons participating in the reaction and F is Faraday’s constant equal to 96485 coulomb mol-1

Again, based on the cellular EMF signal, we have the following:

• If cell EMF is negative, the Gibbs free energy is positive and the reaction is not spontaneous.

• If the EMF pool is positive, the Gibbs free energy is negative and the reaction is spontaneous.

Predicting the final product of a redox reaction

If we only get the reactants of the reaction, we can calculate the final product of the reaction as follows. 

We write out the standard electrode potential values for each reactant using the electrochemical series. Then we see which one has the highest and lowest reduction potential. Once we have these values, we can predict the final product as follows: 

• The ion with the highest reduction potential is reduced at the cathode. 

• The ions with the smallest reduction potential are oxidised at the anode. 

Oxidised and reduced ions give us the final product of the reaction.

Conclusions

The electrochemical series is also called the active series in chemistry. The elements listed in the periodic table are arranged in such a way that they represent an ascending order of electrode potential values. Standard hydrogen electrodes are used to monitor the potential of various electrodes. Depending on the degree of ability to undergo oxidation or reduction, different ions are arranged to form an electrochemical array. Whether metallic or non-metallic. Therefore, the value of the standard electrode potential is calculated by accurately recording the voltage at the end of the standard hydrogen electrode and the half-cell connected to it