comparing magnets and ions

[lemur]

I was thinking about the fact that magnets express polarized electrostatic force (or it seems at least analogous to electrostatic force anyway) and that this may be somewhat analogous to ionization where atoms/molecules become positively or negatively charged in order to electrostatically form chemical bonds. Then I was thinking about the way that magnets can be held in a position that prevents them from aligning their poles and coming together, and that when released from such a fixed position, the magnets will express kinetic energy by rotating and accelerating toward each other and colliding. So then I wondered if chemical reactions such as the burning of hydrocarbons could be analogized to this. I.e. as the bonds between constituent fragments of the hydrocarbon chain are broken, do they become ionized in a way that causes them to shift position and accelerate toward each other leading to collisions that release more energy than was invested in breaking the bonds in the first place?

 

So I guess my two concrete questions about this are: 1) is it valid to think of chemical bonding and reactions in this way, i.e. as reconfiguration of microscopic magnet-like particles that can be separated by energy and caused/allowed to bond again according to ionic attraction? 2) how significant is angular momentum in the transfer of energy between ionized particles as they break away from larger molecules? i.e. is there some way to estimate how much heat released in a chemical reaction (burning) is due to angular-momentum transfers between the re-combining ions and new molecules and how much is transferred through linear motion?

[Horza2002]

Some chemical reactions are indeed ionic in nature. That is one way in which acid catalysis works...for example in ester hydrolysis. The acid protonates the carbonyl of the ester making it more electrophilic (i.e. a greater positive charge). This increase in positive then helps attract a nucleophile (something with negative charge) increase the rate of reaction. Inorganic chemistry (that of metal complexes) is also predominately controlled by electrostatic interactions.

 

Im not 100% sure on the mechanism of hydrocarbon burning, but I don't think it undergoes fragmentation. The mechanism for combustion is pretty complex. Hydrocarbons are have a singlet state whereas molecular oxygen is a triplet. So in this state, they are spin forbidden to react. Normally the initiation step requires a lot of energy to convert the triplet oxygen to the unstable singlet oxygen. Once this happens, a hydrogen atom is abstracted from the hydrocarbon to leave a radical that can then react further with oxygen and the chain eventually falls apart as more hydrogens are removed and bound to oxygen instead.

[mississippichem]

Some chemical reactions are indeed ionic in nature. That is one way in which acid catalysis works...for example in ester hydrolysis. The acid protonates the carbonyl of the ester making it more electrophilic (i.e. a greater positive charge). This increase in positive then helps attract a nucleophile (something with negative charge) increase the rate of reaction. Inorganic chemistry (that of metal complexes) is also predominately controlled by electrostatic interactions.

 

Im not 100% sure on the mechanism of hydrocarbon burning, but I don't think it undergoes fragmentation. The mechanism for combustion is pretty complex. Hydrocarbons are have a singlet state whereas molecular oxygen is a triplet. So in this state, they are spin forbidden to react. Normally the initiation step requires a lot of energy to convert the triplet oxygen to the unstable singlet oxygen. Once this happens, a hydrogen atom is abstracted from the hydrocarbon to leave a radical that can then react further with oxygen and the chain eventually falls apart as more hydrogens are removed and bound to oxygen instead.

 

True, the mechanism of n-alkane combustion is not completely understood. IIRC though, the conversion of oxygen from the doubly degenerate triplet state to the non-degenerate singlet state is in fact the rate limiting step (it can take a while waiting for a random spin pair as entropy doesn't like this much). There is actually some evidence to suggest a pericyclic C-O-O-C transition state [not intermediate!] but this is far from conclusive.

 

Lemur,

 

Though it is somewhat poorly understood, it is known that the combustion of hydrocarbons does not involve ions. It is a radical process, meaning it involves unpaired electrons and no full charge separation.

 

As far as the angular momentum is concerned, do you mean of the constituent electrons? or the angular momentum involved in the torisional and translational movement of the molecule itself?

Edited February 19, 2011 by mississippichem

[lemur]

Some chemical reactions are indeed ionic in nature. That is one way in which acid catalysis works...for example in ester hydrolysis. The acid protonates the carbonyl of the ester making it more electrophilic (i.e. a greater positive charge). This increase in positive then helps attract a nucleophile (something with negative charge) increase the rate of reaction. Inorganic chemistry (that of metal complexes) is also predominately controlled by electrostatic interactions.

Thanks for these terms. They make sense to me and they seem like they could refer to non-ions that still have net-charge. I am slowly learning this stuff, so I was thinking that "ion" referred to any sub-molecular particle with net-charge.

 

Im not 100% sure on the mechanism of hydrocarbon burning, but I don't think it undergoes fragmentation. The mechanism for combustion is pretty complex. Hydrocarbons are have a singlet state whereas molecular oxygen is a triplet. So in this state, they are spin forbidden to react. Normally the initiation step requires a lot of energy to convert the triplet oxygen to the unstable singlet oxygen. Once this happens, a hydrogen atom is abstracted from the hydrocarbon to leave a radical that can then react further with oxygen and the chain eventually falls apart as more hydrogens are removed and bound to oxygen instead.

So combustion is actually initiated by the heating of the oxygen to the point of becoming reactive? Also, what exactly is meant by "triplet" or "singlet?" Are you talking about the bond-strength? Also, by "abstracted," do you mean that somehow a H atom is liberated from the fuel molecule without being completely separated from it? Also, could you possibly directly confirm or deny my assumption that the amount of energy released in a reaction is due to the amount of momentum the particles gain in the process of re-arranging and accelerating due to electrostatic attraction?

 

Though it is somewhat poorly understood, it is known that the combustion of hydrocarbons does not involve ions. It is a radical process, meaning it involves unpaired electrons and no full charge separation.

That's what is meant by valence/co-valence? Could that also be described as electrostatic-driven reconfiguration in that I'm guessing the electrons seek to pair up to somehow balance charge within the orbitals (this may be grasping at straws though - maybe it has to do with mass-oscillation harmonics? Is it known, actually?) Either way, it sounds like the atoms shift around in their configurations within the molecule rather than actually separating and rejoining in new patterns. This almost seems analogous to phase-stability vs. phase-change; or does this confound things even more to start looking at it in this way?

 

As far as the angular momentum is concerned, do you mean of the constituent electrons? or the angular momentum involved in the torisional and translational movement of the molecule itself?

No, I meant the molecule itself. I have always assumed that heat is always the result of linear motion of molecules colliding in a gas, flowing within a liquid, or vibrating in a solid. I never thought about energy being expressed as angular momentum of the molecules and now I'm wondering if that is the case. And, if so, would this mean that spin-energy would result in less volumetric expansion than linear motion of the molecules with the same amount of energy?