Question

What happens to the arrangement of particles during combustion when CO2 is formed?

Answer 1

In chemical reactions, bonds break and new ones form. So let's say you have CH4 + 2 O2 --> CO2 + 2H2O. The 4 single bonds in CH4 break and the double bond in O2 will break. And then C will double bond with two O atoms to form CO2, and 2 H atoms will bond with O to form H2O.

Answer 2

So basically atoms "switch partners"

Answer 3

Adding onto what the previous person said, in the real world bonds don't break consistently or in a direct sequential fashion. Not only that, perfectly complete combustion (as any firefighter can probably guess from experience) isn't complete. Unburnt carbon is one of the primary constituents of "black" smoke seen commonly in oxygen-limited compartment fires (compartment being a technical word something like a room).

At higher temperatures, particularly close to ignition, organic peroxides and acetaldehyde and higher aldehydes are formed in only small amounts. Hydrogen peroxide, carbon monoxide, and formaldehyde are all common incomplete combustion intermediaries that you can detect in a live fire, especially if it's a fire involving diffusion flames (orange flames, as opposed to the blue-ish color of premixed flames such as you might have on your methane gas stove top).

In short, it kind of becomes a wash of chemical activity and greatly depends on factors such as ambient temperature, radiant heat feedback, humidity, and the available oxidizer (normally oxygen, but in explosives this oxygen is actually chemically bound in the mixture or molecules themselves, allowing for split-second reaction of the entire fuel's mass)

If you would like more information on the details of how combustion chemistry works I would highly recommend contacting the BFRL section/department of the NIST (National Institute of Standards and Technology). They might even give you some free information stuff like video DVDs to watch.

Hope this helps answer your question! :-)