Aeroplanes... and more...

CnH(2n+2) + (2n+1/2)O2 >>>>> nCO2 + (n+1)H20

Alright, so it's a bit vague, and the format's all wrong, but hopefully the chemically minded get the gist...

It's the (organic) chemistry of combustion of basic hydrocarbon (alkane) chains. The CnH(2n+1) is the hydrocarbon chain, or - more tangibly (names are simplest isomers from Butane up. Longer chains = more isomers, but end result of combustion remains the same)

C1H(2x1 + 2)        =  CH4        =  Methane
C2H(2x2 + 2)        =  C2H6      =  Ethane
C3H(2x3 + 2)        =  C3H8      =  Propane
C4H(2x4 + 2)        =  C4H10    =  Butane
C5H(2x5 + 2)        =  C5H12    =  Pentane
C6H(2x6 + 2)        =  C6H14    =  Hexane
C7H(2x7 + 2)        =  C7H16    =  Heptane
C8H(2x8 + 2)        =  C8H18    =  Octane
C9H(2x9 + 2)        =  C9H20    =  Nonane
C10H(2x10 + 2)     =  C10H22  =  Decane
C11H(2x11 + 2)      =  C11H24  =  Undecane

And so on and so forth into infinity (well...)

These are also known as paraffins, and are found in most of our oil-based fuels. As a general rule, the thicker the fuel, the longer the chains.

What is the reason for someone who walked out of sixth-form chemistry three weeks before the finals to start talking organic chemistry, you ask?

Jet fuel. 


Jet fuel is a petroleum based fuel, and (although for some reason a lot of people think it's benzene, the wonderful ring hydrocarbon of awesomeness and ourobouros that brightens up every AS-level organic chemistry paper...) it is composed almost entirely of a variety of these simple hydrocarbons (again, keyword Alkane, because sooner or later I'm going to forget that not everyone knows that word).

In burning any alkane, we have the formula I opened with:

CnH(2n+2) + (2n+1/2)O2 >>>>> nCO2 + (n+1)H20

 To give this context, lets talk about methane. With just one carbon, it's the simplest, 

To burn methane, we need one molecule of methane and two and a half of oxygen gas (this is a theoretical burning, so we can have half of a molecule), and we'll produce one molecule of carbon dioxide and two of water. 

So in burning methane (getting swiftly to the crux of this matter) you produce half as many carbon dioxide molecules as you produce water.


At this stage you may well wonder where I'm going with this. 

It ends up at jet trails. And it's less convoluted than you might expect. 


If you burn ethane, with two carbons, you end up producing two carbon dioxides for every water molecule.

Propane produces 3 carbon dioxide, four water. (75%)

Butane produces 4 carbon dioxide, five waters. (


And so it follows. For every Carbon chain you burn, you produce one more water molecule than you produce carbon dioxide.


Now, it may interest you to know that, at fixed temperature and pressure, one mole of any gas occupies the exact same amount of space as another.

This is useful because a mole is a numerically-derived unit, which we can divide by about 602,000,000,000,000,000,000,000 to get to the statement:

"one molecule of any gas at a fixed temperature and pressure takes up exactly the same amount of space".

Now comes the jet fuel/jet trails bit.

The jet trail is formed by water molecules in fuel emissions being spewed out into the pretty-cold atmosphere, where the sudden temperature drop causes them to condense and form clouds. 

While there is a fair amount of Diana Rossing (chain reactions in me-speak) leading to the formation of what eventually becomes a cirrus cloud, while the trail is still a clear line leading from the tail end of the jet, it's still composed mostly of the water from the jet's own burning fuel. 

This is all very exciting, of course.

Along with this water, comes fractionally less of carbon dioxide, taking up fractionally less space. In the best case scenario, with the burning of methane, there is half as much carbon dioxide you can't see being spewed into the sky as there is water that you can see (because it condenses). 

Methane is the best case scenario, and a very unrealistic one at that. In widely used jet fuels, ratios vary but chain lengths hover between 5 and 16 - so CO2 to water ratios at the plane-end hover between 5/6 (83.3%) and 16/17 (94.1%).



So for every jet-trail of rapidly-condensed water vapour across the sky, there's more than three-quarters that volume of carbon dioxide being spewed out, too.


Which, regardless of your stance on global warming, is really quite alarming. 




Go forth and smivel wisely. And cut back on air travel if you'd like coasts to stay roughly where they are...





P.S - This all came about while I was on the train, on the way to my driving theory test (which I aced, by the way), and trying to count the jet-trails etched across Hampshire's blue sky (which I failed to do. And I'm not mathematically impaired). Hampshire's airports combined wouldn't be expected to handle the volume of a recognised international airport such as Heathrow, Gatwick or the likes. Just so y'all know.