[lolwut (OP)]

I was just thinking, the atmosphere is made out of different types of gases right? Most gases have are flammable right? then that means that the atmosphere can be set on fire. does anybody know the temperature needed? Thank you.

[another_someone]

Most gasses are flammable - wrong!

Flammable gasses (such as methane) don't last long in the atmosphere, and there is not much of it in the atmosphere.

The biggest risk of combustion is from organic solids (e.g. animal and vegetable life) that will burst into flame if its flash point temperature is exceeded.

Whet you might get, at very extreme temperatures, if nuclear fusion between the atoms of the gasses in the atmosphere.

[eric l]

Well, there are such things as nitrous oxides.  So a reaction between nitrogen (= greater part of the atmosphere) and oxygen must be possible.  Why does it not happen, not even around a flash in a thunderstorm ?  Or does it need some catalyst that is not available in the atmosphere ?

[another_someone]

Well, there are such things as nitrous oxides.  So a reaction between nitrogen (= greater part of the atmosphere) and oxygen must be possible.  Why does it not happen, not even around a flash in a thunderstorm ?  Or does it need some catalyst that is not available in the atmosphere ?

It exists, but is it an exothermic reaction?

Bear in mind the oxygen and nitrogen in the atmosphere are not monatomic (one could in theory even argue that oxygen can be oxygenated, in that we naturally have diatomic oxygen, so in order to create nitrous oxide, we need to break the diatomic oxygen bond, and the question must be whether we get more energy by bonding oxygen to nitrogen than by bonding oxygen to itself, and nitrogen to itself?).

We do get nitrous oxides in photosmogs, and produced in car engines, so it can happen in some cases; but the fact that this can happen, but does not persist indefinitely, indicates that the N₂ and O₂ in the atmosphere is more stable than NO_x.

[Bored chemist]

I read somewhere that, thermodynamically speaking, all the oxygen should combine with some of the nitrogen and some of the water from the oceans to produce dilute nitric acid. OTOH I think that without the water the reaction isn't so favourable and anyway, it's so slow as to be unmeasurable.

[lolwut (OP)]

So we can't set the atmosphere on fire?

[daveshorts]

No, there are various reactions that will happen if you heat up the atmosphere - oxygen and nitrogen will combine to form NO and NO₂, if you get the conditions right O₂ could produce O₃, but all of these reactions use up energy rather than giving it out so not really burning.

If you put the atmosphere inside a supernova or at the centre of a very old star the oxygen and nitrogen atoms would undergo nuclear fusion to form heavier elements, which would release some energy, but you would need to be hotter and denser than the sun to react at all fast, and not much energy is released, and it isn't really burning.

[eric l]

It was a bit hard to find (well, harder than I expected) but the table you get from this link shows that the formation of nitrous oxides is an endothermic process.  So even if the process could start under some circumstances (like in an internal combustion engine), it does not become a chain reaction.
http://en.wikipedia.org/wiki/Standard_enthalpy_change_of_formation_%28data_table%29

(positive values indicate that you have to add energy to form the compound out of the elementary components)

[that mad man]

I seem to remember some sci-fi stories where the atmosphere caught fire.

Yes I know it was sci-fi but: What percentage of oxygen present in the atmosphere could cause it to burn, or would it be wrong to assume that?

To be honest, I don't know the present concentration of gasses.... [:I]

Bee

[daveshorts]

There aren't any gasses in the atmosphere that will combine with oxygen and release energy, so the atmosphere will not burn whatever concentration of oxygen you have. Things on the ground on the other hand are different. if the oxgen level got to 30% trees, plants, people etc will just burn and you would not be able to put them out.

[ukmicky]

Hi Dave

A while back i was reading about dinosaurs and giant dragon flies etc and remember their was evidence that suggest that 550 million years ago the 0₂ content exceeded 30% and was more than likely around 35%

I believe their is also theoretical modeling and experimental evidence which shows (i believe) the earth would be quite happy at 35% 0₂ and whilst yes fires would burn for longer their would be no great impact on the plant and animal life on earth.

I Will goggle for the details.

[that mad man]

Thanks Dave.

It was the same as what ukmicky said that prompted me to ask.

I had also read that the oxygen levels in the past may have been higher causing dinosaurs etc to be larger.
Trouble is, some plant life was also giant but plants don't rely on oxygen to grow. []

Sorry if that was off topic!

Bee

[ukmicky]

If i remember correctly the high level of O₂ wouldn't have prevented plants from growing but would have changed how big and bold they grew and would have caused a change in how they work bio chemically.

[ukmicky]

I found this. The pdf file is quite big take about 20 secs to load.


http://www.fs.fed.us/ne/newtown_square/publications/other_publishers/OCR/ne_2004_wildman001.pdf

[that mad man]

Thanks ukmicky for the link, an interesting read.  []

Bee