ChemistryPhysical ChemistryElectrochemistryCorrosionTopCorrosionIt’s not necessary that all redox reactions are part of energy change. You can notice many reactions around you which involve a negligible amount of energy or occurs without change in energy. For example, Silver metal is oxidized when it comes in contact in the atmosphere oxygen or hydrogen disulphide.
The film of sulphide which collects on the metal surface acts as a protective layer for further oxidation of metal surfaces. The tarnishing of silver is just one example of a broad class of oxidation-reduction reactions that fall under the general heading of corrosion. The rust of the metals because of corrosion of the surface is an example of the oxidation reaction.