This reaction is the decomposition reaction in which the molecules of water are decomposing to form oxygen and hydrogen. In an endothermic reaction heat is given to the system and in this reaction the heat is being given to facilitate the decomposition of water. In endothermic reaction heat is on the left side of the equation and in this reaction, 137 kcal are added on the left side of the equation. Heat is always positive in endothermic reactions like the above equation. The overall energy of the products is always above than that of the reactants in the endothermic reactions.