[Rutherford]

What is more accurate to say:
1.An exothermic reaction is a reaction in which the products have a lower energetic content than the reactants. For endothermic is the opposite.
2.An exothermic reaction is a reaction in which more energy is released to the environment than it was used for the activation energy. For endothermic is the opposite.

These are two different statements in two different books. They can't mean the same thing as the products of a reaction can have a lower energetic content than the reactants, but this energy gap could be lower that the activation energy, so the reaction would be endothermic. I would say that 1. is for simplicity and that 2. is the precise one. Correct?

[Borek]

Activation energy doesn't tell anything about whether reaction is exothermic or endothermic, only initial and final state count.

the products of a reaction can have a lower energetic content than the reactants, but this energy gap could be lower that the activation energy, so the reaction would be endothermic.

Nope, such situation is impossible. Compare



Try to draw such a plot for the case you described and see if you can find numbers that will make sense.

[Rutherford]

"Activation energy doesn't tell anything about whether reaction is exothermic or endothermic, only initial and final state count."
That is good with the problems where enthalpy is needed to be calculated, because we deduct the enthalpy of formation of the products and the enthalpy of formation of the reactants.

But here: http://www.google.rs/imgres?imgurl=http://wps.prenhall.com/wps/media/objects/486/498325/FG03_12FR.JPG&imgrefurl=http://wps.prenhall.com/esm_freeman_biosci_1/7/1946/498371.cw/index.html&h=268&w=400&sz=17&tbnid=p-4Lldz_oAjRjM:&tbnh=80&tbnw=120&zoom=1&usg=__3gLcNIHcScC8PoTcvKIJFAqTTXE=&docid=b0nUcG829HshdM&sa=X&ei=eNRmUL6ZKYTHtAabkoDYAg&ved=0CCgQ9QEwAg&dur=4679
is a graph similar to the one in the book that I read the 2. statement from. Ea is bigger than the energy gap between the reactants and the products. Is ΔH=ΔE+Ea or only ΔE? According to your graph it would be only ΔE.

[Rutherford]

I think I understood now. In the graph I posted, some amount of energy was spent (Ea) so that transition state is reached. Then, the same amount of energy is released and an additional amount of energy (that is the energy gap between the reactants and products, or ΔH) is released and the products are made. So, more energy was released than spent, making it an exothermic reaction. All the energy spent is now the activation energy of the reverse reaction.
For endothermic (the graph you posted) Ea was spent, some amount was released, but smaller than the Ea, and the energy gap is ΔH.

This makes both statements true then.