"If the energy input is less than the activation energy there won't be enough energy to start the reaction - so nothing will happen"
But, if you look at the graph for an endothermic reaction we see that the energy input is less than the activation energy yet the reaction continues...why? Or am I just reading the graph wrong?
in both cases, energy is needed to start the reaction.
when referring to a reaction profile (see the attached file), the activation energy is the difference in energy between the energy of the reactants and the peak of the energy in the reaction.
endothermic means that the energy of the products is greater than the energy of the reactants, since more energy is taken in than released. exothermic means that the energy of the reactants is greater than the energy of the products, since more energy is released than is taken in. however, in both cases, energy must be taken in before reaction can start.