A change in which the composition of a substance is altered is called as chemical change. As a result, the original properties get changed and one or more new substances are formed. Burning of paper, rusting of iron, cooking of food. All new substances are formed as a result of chemical reactions, a medicine is the end product of the chain of chemical reaction, photosynthesis, digestion is the chemical reaction, useful materials like plastics, detergents and many more products are formed by chemical reactions only, thus we can say chemical changes are very important in our life.