A few years back I read the following in a Q&A section in a newspaper.
In an experiment, a spring and short length of string is placed in a beaker of acid and a record is kept of the temperature change. An identical spring, compressed and secured with an identical piece of string to the first is placed in another, identical, beaker of acid and the temperature change is recorded.
My memory of the results is a little hazy, IIRC no difference was noted in the change in temperature in the two beakers. The question was, what about the energy in the coiled spring, should it not heat up the beaker it dissolves in?
No answer was given in the months after, so I’ll ask the GQ people, should any difference between the temperature in the two beakers be noticed?
Yes, but measuring it’s the tricky part! You have a relatively small amount of energy, in a system with a high heat capacity, and you’re going to release that energy into the system over a number of hours. This is complicated by the much larger chemical energy release of the dissolution reaction, heat transfers in and out of the beaker, evaporative cooling… I think the energy in the spring will be lost in the noise.
You might do better with a length of piano wire stretched almost to yield point, in a silvered capilliary tube of acid, in a vacuum to preclude heat loss.
For piano wire of yield point 2500 MPa, Young’s modulus 180 GPa and density 7.8 g/cm[sup]3[/sup], the maximum stored elastic energy is ~17 J/cm[sup]3[/sup]. That’s as good as you can get without going to funky materials like whiskers and nanotubes and such. (c.f. 2.3 J/cm[sup]3[/sup] wiki’s figure for clock springs.)
So let’s say we do an experiment with stretched piano wire, in a capilliary in a vacuum. Be very generous and say we can dissolve the wire in ten times its own volume of acid, and treat the acid as water in terms of heat capacity. The expected temperature increase of 17 joules in 10 cubic centimetres of water is 0.4 degrees Celcius, assuming zero heat losses over the time it takes to dissolve. Not much, but probably measurable.
Ah, so basically its not something we could have measured in an A-level class, with simple mercury thermometers in beakers of acid, the change being so small.