An endothermic reaction with high activation energy for the forward reaction is given by the diagram : (a) (b) (c) E E (d)

Reactions which involve absorption of heat energy are called endothermic reactions. For such reactions. P R H H In graphs (c) and (d), the heat of products is more than heat of reactants and thus they represent endothermic reactions. But in (d)only small amount of energy is absorbed(less difference between energy of reactants and products). Thus, (c) represents maximum activation energy. Note : Activation energy is the excess energy that the reactant molecule must possess to cross energy barrier.