INTRODUCTION: Chemical reactions are changes in which some new substances are formed(Dictionary.com) . Substances that undergo chemical change are called reactants, while the new substances are called products. Chemical reactions are very important in chemistry because it allows the possibility of the formation of different useful new substances. Chemical reactions can be divided into four reactions which are namely synthesis single displacement, double displacement and decomposition reactions. Firstly, the concept of synthesis reaction which is when two or more simple compounds combine to form a complicated one. For Example: Formation of CO2, i.e C(s) + O2(g) ----------- CO2(g). Secondly, Decomposition reaction, which is the opposite of synthesis reaction is when a complex molecule breaks down to make simpler ones, it2 mostly requires heating. An example can be seen in the electrolysis of water i.e 2H20(g)---------- 2H2(g) + O2(g) . Thirdly, the single displacement reaction, which is when one element trades places with another element in a compound, it is mostly associated with the electrochemical series i.e the electrochemical series serve as the rules for the displacement of the elements in the reaction. An example of this type of reaction is between zinc and hydrochloric acid. i.e Zn + 2HCl ----------- Zncl2(aq) + H2(g).(Hand out on chemical reactions.) .......Finally, double displacement reaction, which involves the exchange of cations between two ionic compounds usually in an aqueous solution. It is also referred to as double replacement reaction. For example, the reaction between sodium nitrate and magnesium sulphate. i.e 2NaNo3 + MgSo4---------- Na2So4 + Mg(No3)2 .