Answer:-The chemical reactions in which heat is evolved, are called exothemic reaction.e.g;when carbon reacts with oxygen,carbondioxide is produced along with a lots of heat which is an exothermic reaction.The reaction can be written as:- C + O₂ -----> CO₂ + Δ (heat).The reactions in which heat is absorbed are called endothermic reactions.e.g;When calcium cabonate (CaCO₃) is heated it splits up into calcium oxide (CaO) and carbon dioxide absorbing lots of heat and the reaction is termed as an endothermic reaction,which can be shown as:- CaCO₃ + Δ (heat) -----> CaO + CO₂