energy "destroyed"? Energy as a rule cannot be destroyed, right? then please look at this- i take a spring of high spring constant and compress it. then i take a smaller spring and fix it in such a way in the larger spring that it retards the expansion of the larger spring. then i leave the springs in this state so that they have a good amount of potential energy. then i take identical spings but i dont add potential energy to them. now i drop these seprate set-ups in acid solutions so that the springs dissolve. the amount of hydrogen liberated from both set ups is the same. the final energy liberated by both the systems is same, and the springs are no more. it is quite clear that both spring setups had same matter initially. then has the potential energy i had given to the first spring system been destroyed?