Thermodynamics & Electrode Potential

Corrosion in aqueous solution has been found to involve electron or charge transfer. Thermodynamics given an understanding of the energy changes involved in the electrochemical reaction of corrosion .these energy changes provide the driving force and controls the spontaneous direction for chemical reaction , thus thermodynamics tell us about tendency for the reaction to occur but cannot predict the rate of reaction.

A conducting metal containing mobile electrons forms a complex interface in contact with an aqueous solution. unsymmetrical polar H2O molecules ( H-atom positive , O-atom negative ) are attracted to the conductive surface , forming an oriented solvent layer , which prevents close approach of charged species (ions) from bulk solution. Charged ions also attract their own sheath of polar water-solvent molecules which further insulate them from the conducting metal. The plane of closest approach of positively charged cations to the negatively charged metal surface is often referred to as the outer Helmholtz plane the result is an interfacial structure of separated change commonly referred to as the electrical double layer which behaves experimentally much like a charged capacitor