Comment by dekhn

8 years ago

A long part of my scientific career has been unpacking simple statements about things like bike riding, and finding the underlying process is subtle, and reveals many interesting things.

When I was a kid, I had a teacher who said that cutting paper wasn't a chemical change- no bonds were broken. That seemed odd to me, but after I had a PhD, I understood a few things better. That when you cut paper, mostly hydrogen bonds- bonds, but a particularly weak form of bonds- are broken, but threre is enough kinetic energy to break some covalent bonds too. This turns out to have huge implications (besides the fact that the teacher was wrong).

11 comments

dekhn

Reply
logfromblammo  8 years ago

If you smash a salt crystal with a hammer, all the resulting pieces end up with equal charges of anions and cations, so were any ionic bonds really broken?

That covalent bonds are broken seems obvious if you ditch the paper and cut through a sheet of long-chain polyethylene. The scissors don't just stop if they're about to break a polymer chain.

  • dekhn  8 years ago

    I think even the salt crystal will have some ionic bonds broken- smashing it with a hammer should generate a bunch of kinetic energy which converts to heat, some of the heat will exceed the ionic bond strength, and break bonds.... right?

  • rocqua  8 years ago

    How tiny of a charge is so small as to be unnoticable?

    Certainly, if an object millimeters across has a charge of 1 electron that isn't noticeable.