In nature, we come across temporary, permanent, natural and man made changes. A permanent change in which new substance or substances formed with completely unlike those of the original substances is called a chemical change. Chemical changes are represented by formulae or equation is known as chemical equations. All the chemical equations must balance, because atoms are neither created nor destroyed in chemical reactions.
Chemical reactions are generally of four types; they are
4.Double Displacement Reactions.
Oxidation is a reaction that involves the addition of oxygen or removal of hydrogen. Reduction is a reaction that involves the addition of hydrogen or removal of oxygen. If oxidation and reduction occur in the same reaction, such reactions are called oxidation – reduction reactions or redox reactions.
When some metals are exposed to moisture, acids etc, they tarnish due to the formation of respective metal oxides on their surface. This process is called corrosion damage to car bodies, bridges, iron railings, ships etc., and to all other objects that are made of metals. Especially corrosion of iron is a serious problem. Corrosion can be prevented by shielding the metal surface from oxygen and moisture. It can be prevented by painting, oiling, greasing, galvanizing chrome plating or making alloys. When food materials that were left for a long period, the fat/oil containing in food materials oxidized and become rancid.
The spoilage of food can be prevented by adding preservatives like vitamin C and vitamin E. Keeping food in air tight containers helps to slow down oxidation process. Manufactures of potato chips flush bags of chips with nitrogen gas to prevent the chips from getting oxidized.