Chemical changes are a result of chemical reactions. All chemical reactions involve a change in substances and a change in energy. Neither matter or energy is created or destroyed in a chemical reaction---only changed. There are so many chemical reactions It is helpful if we classify them into some general types like combination reactions, decomposition reactions, displacement reactions and redox reactions. 

Chemical reactions always involve a change in energy. Energy is neither created or destroyed. Energy is absorbed or released in chemical reactions. Chemical reactions can be described as endothermic or exothermic reactions. In this chapter we will study about these various reactions, how to represent them by using chemical equation and how to balance these equations?