Where does the spring's energy go ?

[joo]

I can't get my head around this problem : Consider a stretched spring, fixed by string at the both ends to a bottle. The bottle is filled with a certain acid, that only eats away the spring and not the string.

Assume the ideal conditions - the whole spring gets dissolved completely at the same time. Where does the potential energy go ?

There is an overview of the problem in the attachment.

 

[Simon Bridge]

Kinetic energy in the products of the reaction.
Heat and so on as well.

You should consider how energy gets stored in the spring, and what actually happens when acid dissolves it... on the atomic level.