Changes taking place around us are mainly categorised into two kinds. These changes are
A chemical change is a change that occurs when the internal structure of a material is altered to generate a new substance. For example, chemical changes can occur during the digestion of food, the burning of wood, the baking of a cake, the curdling of milk, the mixing of acid, the boiling of an egg, the rusting of iron, and so on.
Chemical changes/reactions are the processes through which two substances chemically react to form a new substance with different chemical properties. All new substances used in different fields and our daily lives are products of chemical changes.
The above chemical change can be represented by the following chemical equation:
Magnesium (2Mg) + Oxygen (O2) → Magnesium oxide (2MgO)
Further, the powdery ash, Magnesium oxide is mixed in the aqueous solution resulting in the formation of a new substance. The mixture obtained is basic in nature.
Copper sulphate solution (blue) + Iron → Iron sulphate solution (green) + Copper (brown deposit)
CH3COOH (aq) + NaHCO3 (aq) → CO2 (g) + H2O (l) + CH3COONa (aq)
The gas obtained in this chemical change is further passed to lime water solution and hence the reaction between carbon dioxide and lime water yields the following chemical substance.
Carbon dioxide (CO2) + Lime water [Ca (OH)2] → Calcium Carbonate (CaCO3) + Water (H2O)
The new chemical substance formed here is calcium carbonate (CaCO3). This calcium carbonate makes lime water milky. Turning lime water into milky is considered as the standard test of carbon dioxide.
In the above-mentioned examples of chemical reactions, it has been seen that one or more new substances are produced in a chemical change. Besides these newly formed substances, the following may accompany a chemical change-
4Fe + 3O2 +2H2O → 2Fe2O3.H2O(Rust)
For rusting, it is essential to have both oxygen and water. If there is more humidity in the air, then the process of rusting increases. As iron is used in making bridges, ships, cars, truck bodies and in many other substances, rusting of iron leads to monetary loss as it corrodes the iron.
Rusting of iron can be prevented by not allowing iron to come in contact with the moist air. Coating iron with oil, grease or paint is the simplest method to prevent the process of rusting.
Another way to prevent rusting is coating iron with another metal such as zinc or chromium. Iron pipes used in home to carry water are galvanised to prevent rusting.
As we know, there is a huge demand for iron in the shipbuilding industry. The body of the ship is always in contact with water and the air. The salt in water speeds up the process of rusting. Use of stainless steel can help to prevent the process of rusting.
Chemical changes are important in our lives. We often see burning of wood or leaves, burning of coal is also a chemical change. The process of burning is always accompanied by the production of heat and light.
Let us consider a few examples showing chemical changes in our everyday life.
From the above discussion, we understood that chemical reactions happening around us are very important in our lives. Formation of new substances occurs as a result of chemical change. Digestion of food, fermentation of grapes, etc. all happen due to chemical changes. A chain of chemical reactions yields the production of several new substances. Useful materials used in our daily life such as plastics and detergents are produced as a result of chemical reactions. Indeed, new substances are produced by studying chemical changes.