What do you understand by exothermic and endothermic reactions?

Heat evolving reaction are known as exothermic reactions. In these reactions Heat is released when reaction starts. The energy needed to initiate the reaction is less than the energy needed given from the reaction.

In reaction where heat is absorbed are known as endothermic. The heat energy is gained from the atmosphere in this reaction. The heat required to initiate the reaction is fairly high than the heat given from the reaction.