The energy is actually converted into mass, by the famous E = mc^2 formula. If you weigh the total acid plus spring (plus rubber band) before and after, you’ll find more mass after the acid has done its trick, especially if it’s a Catholic mass. If it’s not a Catholic mass, but you’re doing the experiment in Boston, the energy would of course have been converted into Boston, Mass. If the experiment were done in April, you could say that there was spring (with rubber band) in the air in Boston, Mass. However, trying to weigh the whole of Boston before and after the experiment is considered too difficult.
Oh, wait, man, I bet you didn’t mean that kind of acid, like, wow.