Monday, August 4, 2008

a thought experiment

here is a little gedankenexperiment for you:

Leave your answer in the comments!

[1] Let's assume that the clamp is impervious to acid, and keeps the spring in the same position until it is dissolved.


Anonymous said...

Wow, that is a great question. Here are my thoughts:

Some of it still will be converted into kinetic energy. As 'bits' of the spring dissolve, this will leave more space between the clamp and the spring, so there will be some expansion.

However, this seems like a relatively small amount. Acid dissolving metal is an exothermic reaction; could it be possible that more heat would be created, since there is energy present in the spring?

Chemically, I would no, because it's the same amount of metal regardless of its orientation, but physically, I would say yes...

For some reason, I'm going to trust my physics instincts and say that it will be hotter; I'm gonna have to look into this however.

Joel Kelly said...

Here's what I think:

The compression has to manifest itself someway on the atomic level. Strained bond lengths or angles, increased vander Waal's forces from non-bonding atoms, whatever.

In some way, there has to be a slightly more unstable chemical species. This species could react quicker with the acid, lowering the activation energy for dissolution and leading to a net increase in heat.

Another question that my lab mates and I argued on: is a compressed spring lower or higher in entropy?

Anonymous said...

Nice; better chemical analysis than I could come up with.

As for the entropy issue, I would naturally think entropy would be higher in a uncompressed spring; compressing it puts it a higher order I'd think.

Additionally, to keep the spring compressed, you need a clamp in place, and placing the clamp puts 2 pieces together, which decreases entropy.

I'll ask around the lab tomorrow and report back on other thoughts. Btw, what's your name?