Another where did the energy go question

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Discussion Overview

The discussion revolves around the energy balance during the collision of two hydrogen atoms, exploring where the kinetic energy goes when they form a molecule of H2. It addresses concepts of kinetic energy, bond energy, and potential energy in molecular interactions, with implications for both theoretical understanding and practical examples.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant notes that the system has positive kinetic energy due to the motion of the atoms, but the momentum is zero because the momenta cancel each other out.
  • Another participant suggests that some of the kinetic energy is converted into bond energy when the atoms form H2, but questions where the remaining energy goes.
  • One response proposes that the extra energy may be stored as kinetic or potential oscillation within the molecule, likening molecular bonds to springs.
  • Another participant mentions that if the collision is not head-on, the H2 molecule could also gain rotational kinetic energy.
  • One participant argues that energy is likely lost as heat during the collision, comparing it to the behavior of colliding balls that "squish" and generate heat.
  • There is speculation about the possibility of photon emission during the collision, but this remains uncertain.

Areas of Agreement / Disagreement

Participants express various hypotheses about the fate of the kinetic energy, with no consensus on a single explanation. Multiple competing views remain regarding the mechanisms of energy transformation during the collision.

Contextual Notes

Participants acknowledge limitations in their understanding and the lack of definitive sources to support their claims. There is also mention of potential upper bounds on energy storage in molecular oscillations, but this remains unresolved.

Who May Find This Useful

This discussion may be of interest to students and enthusiasts of chemistry and physics, particularly those exploring molecular interactions and energy transformations at the atomic level.

jhicklin
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Another "where did the energy go" question

I am struggling with a simple energy balance concept.

Two atoms, say Hydrogen, are traveling straight at each other with equal velocities.

This system has positive kinetic energy due to the motion of the atoms, but the momentum of the system is zero since the momentums of each atom cancel each other.

Now, the two atoms collide and (assuming the kinetic energy exceeds the bond energy) form a molecule of H2.

To conserve momentum, the velocity of the newly formed molecule must be zero, and so its kinetic energy must also be zero.

Some of the (prior) kinetic energy now exists as the bond energy of H2, but where is the rest?

If we were talking about two lumps of clay, we would say the extra energy had been converted to heat, but when we get down to individual atoms, that answer isn't satisfying.

I want to say that the extra energy is stored as kinetic/potential oscillation within the molecule, but I haven't been able to find a reliable source agreeing with that. Also, this would imply an upper bound on the amount of energy that could be stored in this fashion, but I don't see discussion of that in chemistry books.

I imagine my freshman chem prof explained this, but I can't remember and I can't find an explanation in a text.

Thanks for any clarity or pointers to references talking about this.
 
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Photons?
 


Molecular bonds act a lot like springs (in that there is an equilibrium position and the force increases quadratically the farther the bond is strained from that). Some of the energy will probably go into harmonic motion of the bond.

Also, if the collision is not head on, the H2 molecule will rotate, having rotational KE.
 


Even at atomic levels, you do lose energy to heat. That is probably the most likely place it has gone. When two things go hit each other such as two balls the balls will "squish" until the merge together, in this squishing they are rubbing together causing heat. Unless they hit at an angle they would probably not be moving much. There could be some sort of ocilation happening aswell. And i don't know if photons could be emitted


FoxCommander
 

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