Exothermic Reaction Origin: What is the Source?

[Farside]

what is the origin of the engery liberated in an exothermic reaction? I've been hitting the books for this but can't find it. Seems simple enough though. I just need to be sure.

 

[so-crates]

Its a form of potential energy that is stored in the bonds of a molecule.. Think of a mouse trap.

 

[DeathKnight]

Bond making is an exothermic reaction (opposite of bond breaking in which energy must be applied to break the bonds). If there is a reaction in which more bonds are made than bonds broken than it is an exothermic reaction. The reaction in which weak bonds are broken and strong bonds are formed is also an exothermic reaction.
Hope this helps.
Ab S.

 

[chem_tr]

I'll give an example, maybe this will clarify something.

Sulfuric acid dissolves in water with evolution of great amounts of heat. In here, as DeathKnight and so-crates said, some bonds are broken and their energies are evolved as unused energy. This can be explained in another point of view, sulfuric acid dissolved in water has a lower energy, thus more stable than its non-aqueous counterpart. This results with an energy flow outside, what we call as "exothermic" reaction.

In biological sytems, phosphorus-oxygen bond cleavages, as in ATP and ADP, etc., are used frequently, since it gives great energy gain. Adenosine triphosphate can be regarded as an "energy bank", which releases energy upon "application".