Naked Science Forum

Non Life Sciences => Chemistry => Topic started by: lolwut on 27/06/2007 20:46:30

Title: At which temperature does the earths atmosphere burn?
Post by: lolwut on 27/06/2007 20:46:30
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.
Title: At which temperature does the earths atmosphere burn?
Post by: another_someone on 27/06/2007 21:56:04
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.
Title: At which temperature does the earths atmosphere burn?
Post by: eric l on 28/06/2007 14:14:58
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 ?
Title: At which temperature does the earths atmosphere burn?
Post by: another_someone on 28/06/2007 14:46:42
Quote from: eric l on 28/06/2007 14:14:58
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 NOx.
Title: At which temperature does the earths atmosphere burn?
Post by: Bored chemist on 28/06/2007 21:11:56
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.
Title: At which temperature does the earths atmosphere burn?
Post by: lolwut on 29/06/2007 00:47:24
So we can't set the atmosphere on fire?
Title: At which temperature does the earths atmosphere burn?
Post by: daveshorts on 29/06/2007 09:20:27
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.
Title: At which temperature does the earths atmosphere burn?
Post by: eric l on 29/06/2007 10:57:41
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)
Title: At which temperature does the earths atmosphere burn?
Post by: that mad man on 29/06/2007 21:14:30
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
Title: At which temperature does the earths atmosphere burn?
Post by: daveshorts on 29/06/2007 22:19:37
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.
Title: At which temperature does the earths atmosphere burn?
Post by: ukmicky on 29/06/2007 23:11:05
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.
Title: At which temperature does the earths atmosphere burn?
Post by: that mad man on 30/06/2007 18:59:07
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


Title: At which temperature does the earths atmosphere burn?
Post by: ukmicky on 30/06/2007 23:04:36
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.
Title: At which temperature does the earths atmosphere burn?
Post by: ukmicky on 01/07/2007 14:53:07
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
Title: At which temperature does the earths atmosphere burn?
Post by: that mad man on 01/07/2007 15:02:58
Thanks ukmicky for the link, an interesting read.  [:)]

Bee