Springs and acid

[Dave5N]

RE: the compressed spring would be very slightly more exothermic - I meant the exothermic energy of the acid reaction with the compressed spring could be greater than that of the uncompressed spring - I should learn to write more clearly

Why can the enthalpy of the bonds not be increased when the spring is compressed?

I've asked some clever bods because I like these sort of puzzles, They like the conversion to kinetic fragments idea, which I hadn't fully understood from your first post Dave,

BUT

Consider when the compressed spring is only partially dissolved - before it snaps.

A thinner spring produces less energy when expanding than a thicker one, hence it stores less potential energy when compressed. Our partially dissolved (now thinner) spring has therefore lost some energy somewhere?

The 'enthalpy of the bonds' - chemical energy, is not affected by the mechanical potential energy stored in the spring.

The partially dissolved spring (actually oxidised) has partially lost potential kinetic energy as I described earlier.

In fact, thinking about it the kinetic energy in a sense is still kinetic energy, just more randomised. Thermal energy is really just kinetic energy at a molecular scale, and is random in direction.

 

[bonj2]

Same pressure bonj. The example talks about a clip.

You have to maintain the same amount of pressure. What happens?

The structural integrity of the ruler is weakened until it can't take it no more. Then it fails at the weakest point. And that's where your energy goes.

I propose that the same would happen to a spring being eroded by acid.

yeah, ok. But it would be boring. It wouldn't explode in a shower of sparks.

 

[bonj2]

A lot more what? Are you unfamiliar with the first law of thermodynamics?

<valid scientific analogy>
The same amount of general effort. If you compare potential energy with kinetic energy, think how high up you would have to go for ALL of it to be converted into thermal energy. You would have to go pretty high up in order to be completely burnt up before you hit the ground. A lot higher than the tallest building, probably right up into space. If you only went up say a mile, you wouldn't be completely burnt up and so a lot of the energy would still only be kinetic energy when you were incident upon the earth.
</valid scientific analogy>

NO it's not converted into heat.

Heat is created as the spring is compressed - this is the inefficency of the compression process. It takes say 1J to compress it but the spring only stores 0.8J the 0.2J difference is lost as heat.

However the compressed spring still has 0.8J of stored potential energy and assuming the spring cannot at any stage change shape this has to go somewhere.

Probably as heat, but none of the mechanisms proposed so far allow for it. Dissolving a metal in acid is an exothermic reaction, so maybe the compressed spring would be very slightly more exothermic - This could be tested in a very sensitive calorimeter, but would be very hard to do.

gbb - "infers that at some point, the original amount of acid wasnt, or wouldnt,be enough....but of course, it would be enough..."

Why of course?

this is exactly what i meant with my first reply just worded a bit better. (apart from the bit about heat being lost during compression which is irrelevant.)

 

[Dave5N]

<valid scientific analogy>
The same amount of general effort. If you compare potential energy with kinetic energy, think how high up you would have to go for ALL of it to be converted into thermal energy. You would have to go pretty high up in order to be completely burnt up before you hit the ground. A lot higher than the tallest building, probably right up into space. If you only went up say a mile, you wouldn't be completely burnt up and so a lot of the energy would still only be kinetic energy when you were incident upon the earth.
</valid scientific analogy>




this is exactly what i meant with my first reply just worded a bit better. (apart from the bit about heat being lost during compression which is irrelevant.)

If you used up all the kinetic energy before you hit the ground you wouldn't hit the ground.

 

[bonj2]

If you used up all the kinetic energy before you hit the ground you wouldn't hit the ground.

before you WOULD HAVE hit the ground if you hadn't burnt up then

 

[freakhatz]

The clip would regain the potential energy it had lost due to holding the distorted spring.

 

[Dave5N]

D'oh!!!

5 pages and then the simple answer.

Shame it is wrong!