In a normal room with normal levels of oxygen, and without any testing or experimenting, how could you tell if a substance burns with complete or incomplete combustion???

it would leave no solids behind, and become pure gasseous products.

incomplete would leave a product, even if it were only ash that fell later as dust

 

OK, i think a minor misundstanding. Lets say, you have an alcohol, propanol and it is involved and a combustion. How can u tell, without looking at a balanced formula at room oxygen levels, wether it is imcomplete or complete combustion.

 

You only have the name of the chemical and two options for a formula, complete or incomplete

ok, if the fuel contains elements that AFTER reaction with the Oxygen (in the air) do not form to make a gas, then the combustion is STILL complete (providing all the fuel has reacted). IF there are particles in the air as dust like Soot (carbon) then it`s incomplete as Carbon will combine with air.

 

So....

A: all fuel must have reacted

 

B: any reactants left over that COULD HAVE combimed to form a gas is Incomplete.

 

C: reactants left over that CANNOT combine with Oxygen, but conforms to A will be considered complete.

 

hows that dude

But how could you tell how it would normally combust, as there are two ways it can go

by the way, there is no experimenting !!!!

well for a start we can elliminate the AIR thing and just call it Oxygen, as that`s the only thing in air that plays a part at standard RTP, and assuming there is sufficient quantity of Oxygen to complete the reaction.

 

It seems I`m trying to get to the actual question here, or a clear definition of it at least!? you don`t HAVE to experiment to work it out, it wasn`t suggested. it can be done on paper only

 

Well let me explain this scenario:

 

1. You are given a hydrocarbon

2. You cannot experiment to see whether soot is released

3.You have to find out whether is burn completely or incompletely

4.This is ALL at normal room oxygen levels i think 30%

 

How can u tell whether it burns completely (Water and co2 released) or whether it burns incompletely (water, co2, co and C released)

sure can, take a look at post #4 here:

http://www.scienceforums.net/forums/showthread.php?postid=28271#post28271

 

hope that helps somewhat?

 

ps: it`s 21% Oxygen in Air (unless you live in L.A) LOL

 

lol

 

well no, not really LOL

 

because it can either burn completely or incompletely

 

i want to know how it would burn NATURALLY

and to aid that, i want to know how much oxygen for a reaction is that maximum possible at room ixygen levels so that it changes from being a complete to incomplete combustion

huh?

 

that`s IS how it would naturaly combust, unless the room ran out of oxygen, that`s what it would do

then, when does it combust incompletely if we have all the oxygen we want (from the room) ????

 

Sorry to bother u, but, i can't really get to grasp with this

it would burn incompletely in the lack of sufficient Oxygen.

think of a badly tuned car engine or a gas heater... OR even better a bunsen burner!

you open the nozel to let more air in at the base of it and you get a BLUE hot flame

close it, and it goes yellow and sooty

yeah, but at normal room oxygen levels, why does a combustion of lets say benzene is incomplete?

the combustion of benzene need not be incomplete in 21% oxygen, it all depends on the apparatus used in its combustion

think bunsen burner flame

no, but if u take an evaporating basin, and light benzene in it, it burns incompletely

 

In an equation, is there a certain amount of oxygen that is too high so that it burns incompletely, something like 9o2 or something, that forces it to burn incompletely???

in that type of scenario yes, you`re limited by physical factors in the delivery of Oxygen within a given time frame, hence the need for Oxygen delivery apparatus and mixing systems

so, if there is a large area of benzene exposed to the air, it would burn completely

no, that would be self defeating, as the air coming in from the outside would have it oxygen expired as it passed the edge of the burning tray and be useless for the fuel in the middle.

so then, what makes it combust imperfectly? What aspect of it?

no reaction is every 100% efficient, its just the nature of things.

oh ok. i just wanted to know whether it was possible, i got my answer: NO! lol

ooooohhhhh ooooooohhhh weee

 

consider this...

 

standard aviation fuel, I can light a match and throw it in a pool of this fuel, the match will go out and there will be no fire.

heat this fuel to just bellow "flash point" and do the same, and Whooosh! it`ll burn

now add pure Oxygen into this equasion and it`ll more than likey explode!

 

 

so HEAT and OXYGEN DELIVERY is critical for total and complete combustion

oh yeah, and Pressure also plays a role, but the above 2 are the main protagonists

oh, ok now , i got it. Thanx