Introduction

It is a common observation in everyday life that many processes taking place around us involve chemical changes. These are some type of chemical reactions. In such reactions, there are some reactants which eventually change into prod- ucts. During these transformations, the atoms of the elements remain the same but they are rearranged. In them, the old bonds are broken and new bonds are formed . This leads to formation of new products. These chemical reactions are accompanied by some typical observations such as evolution of a gas or energy, change of state or colour, formation of a precipitate etc. For convenience, these chemical reactions have been classified into some broad categories. The classification is not very exclusive i.e. the line of demarcation in them is not very sharp. Sometimes one reaction can also be classified under two headings. But even then, the classification helps to understand the nature of reactions better.