This is pretty old but I never could find a satisfactory answer…
“You compress a spring & dissolve the spring in acid. What happened to the energy in the spring?”
Hopefully, we’ll have at least two answers that agree 
thx
It’s released as heat as the spring dissolves.
It can become sound energy.
What was compressing the spring? Your fingers? In that case, when the middle of the spring dissolves, your fingers snap shut, sending shards of acid-laced spring metal deep under your fingernails. Then, you yell.
That’s pretty much it. The first answer is right if the spring dissolves perfectly evenly and the second is right if it doesn’t.
As a rule of thumb, when the question is “what happens to the energy”, the answer is almost always heat. It’s very easy to convert any other form of energy to heat; in fact [oversimplification]the Second Law of Thermodynamics says that it’s bound to become heat eventually.[/oversimplification]
Konrad
Do you think Chronos would let me use “rule of finger,” when it all gets converted to sound energy instead of heat energy?
Rule of finger: Don’t stick your hand in acid while holding a spring.
Also, don’t stick your hand in acid when not holding a spring.
I think the thumb wins; even sound energy eventually ends up as heat.
Right I should have said that you secure the spring compressed with some more wire. Still, I don’t see where the heat comes from.
Assuming the spring won’t sproing due to a non-dissolving wire or whatever, I assume the potential energy is “stored” in the microscopic bits o’ metal that make up the spring (not atomic scale). Those bits want to return to their normal position (sprung) and as they slowly dissolve, the energy is released as heat from between the neighboring bits. That way, the energy is slowly released to the acid along with the dissolved portions, without having the entire spring bounce back to its normal state all at once.
This is the funniest thing I have read in some time.