a)An endothermic reaction takes place when a great amount of energy is needed to break the existing bonds in the reactants. It means that an endothermic reaction needs or takes in energy to continue.example:In a test tube, when a small quantity ofammonium chloride(NH4Cl) is dissolved in water, the tube becomes colder. Heat is absorbed from the surroundings during the chemical reactionNH4Cl(s) + H2O(l) →→ NH4Cl(aq) – heat.b)A combination reaction is one in which two or more reactants combine to form a single product.Examples:formation of calcium oxide by the combination elements calcium and oxygen.2Ca + O2→2CaOc)Abalanced equationis anequationfor achemicalreaction in which the number of atoms for each element in the reaction and the total charge are the same for both the reactants and the products.example:6 CO2+ 6 H2O → C6H12O6+ 6 O2(balanced equation forphotosynthesis)d)Displacement reaction is a chemical reaction in which a more reactive element displaces a less reactive element from its compound. Both metals and non-metals take part in displacement reactions.example:Fe + CuSO4 >>>>>>FeSO4 +Cu