Question

Write short notes on:
A.Nernst equation
B.Corrosion

Answer 1

Electrochemistry is a wide subject and Nernst equation and corrosion are a part of it. The Nernst equation is used to calculate the cell potential of an electrochemical cell at any given temperature, pressure, and reactant concentration. Corrosion is an electrochemical process as it involves redox reactions between the metal and certain atmospheric agents.

Complete step by step answer:
(i)The Nernst equation gives a relation between the cell potential of an electrochemical cell, the standard cell potential, temperature, and the reaction quotient. The cell potentials of electrochemical cells can be determined even under non-standard conditions with the help of the Nernst equation.
Nernst equation is an equation which relates the capacity of an atom or ion to take up one or more electrons and measure reduction potential at any conditions to that measured at standard conditions i.e. standard reduction potentials at 298K, one molar and one atmospheric pressure.
${E_{cell}} = {E^0} - [RT/nF]\ln Q$ is the Nernst equation that we study in electrochemistry.
Here, ${E_{cell}}$ is the cell of potential of cell
${E^0}$ is the cell potential under standard conditions
R is the universal gas constant
T is temperature, F is Faraday constant, Q is reaction quotient and n is the number of electrons transferred in the redox reaction.
For a reduction reaction in case of single electrode potential ${M^{n + }} + n{e^ - } \to nM$ , Nernst equation becomes:
${E_{red}} = {E^0}{M^{n + }}/M - [2.303RT/nF]\log \dfrac{1}{{[{M^{n + }}]}}$

(ii)Corrosion is defined as the natural process that transforms pure metals into undesirable substances reacting with substances like water or air. This causes damage and disintegration of the metal beginning from the portion of the metal which is exposed to the environment and then spreading to the entire bulk of the metal.
Metals which are located higher in the reactivity series such as iron, zinc, etc. get corroded very easily and metals positioned lower in the series like gold, platinum and palladium do not corrode. We know that corrosion involves oxidation of the metals and as we go down the reactivity series tendency to get oxidised becomes very low.
There are many factors that affect corrosion. These are: exposure of the metals to gases present in air and to moisture like salty water. They increase the rate of corrosion. Presence of impurities like NaCl also affects it. An increase in temperature and presence of acid in the atmosphere leads to increase in corrosion.

Note:
We cannot use Nernst equation to measure cell potential when current is flowing through an electrode because current affects the activity of ions on the surface of the electrode. We can prevent corrosion by many methods such as electroplating by coating it with any other metal, cathodic protection by using more reactive metal, galvanizing with zinc layer, painting and greasing.