[kevinnn]

i did some web searches but i could not find an answer.  why is gasoline so flammiable, why are some liquids not flammiable, i just dont understand this whole concept.  any help would be great, thanks . 

[typhoon2028]

Try researching vapor pressure, auto ignition temperature, and flash point.

There are many materials considered more flammable then gasoline.

[darko]

on the lavel of your question, liquids in general, are not flamable, the vapor is ,so liquids as such do not burn , but vapor yas, so you should start with suggestions ofered by typhoon.

then you should find answer wath in general "burning" is, and you will soon find why some solids (e.g. Na, example,becouse is easy to find answers), are more flameble then some "liquids" , and some gasses are not, at conditions simillar as gasoline is

p.s. once again, the answer is based on level of question,

[408]

Flammability comes from the ability to be oxidized, and generally in our environment, by gaseous oxygen.  For simplicity we will avoid discussing flammability in atmospheres of F2 etc.

Ease of flammability is related to vapour pressure, and how easily the compound is oxidized.  Short chain hydrocarbons are of high volatility, where as longer are less volatile.  Something like pentane will ignite from a flame even if the flame is nowhere near the surface of the liquid due to the high concentration generated in the air above.  Heavier hydrocarbons such as diesel can be poked with a lit match without igniting.  (I have done this with biodiesel, but not with real diesel, and have heard they behave similarly, if not someone can correct me)

I would not call sodium more flammable than gas...I have tried to light it several times without ignition, even including throwing 10g or so into a campfire.  Just melted and oxidized.  The only way to really get it going is to  drop it onto a puddle of water, so the hydrogen ignites, and the ball of molten Na escapes from the solution surface, followed by rolling over a dry surface while molten, igniting soon after it leaves the water surface.

[darko]

I would not call sodium more flammable than gas...I have tried to light it several times without ignition, even including throwing 10g or so into a campfire.  Just melted and oxidized.  The only way to really get it going is to  drop it onto a puddle of water, so the hydrogen ignites, and the ball of molten Na escapes from the solution surface, followed by rolling over a dry surface while molten, igniting soon after it leaves the water surface.

It is not compared to gasoline, but some other "liquids",  so it is just example to think that flamebility is not necesary releted to gases, solids or liquids as such but there some other factors

[Enthalpy]

I confirm experimentally plain Diesel oil can't be lit at room temperature in air with a lighter. It needs a wick.
Kerosene is near the limit of what can be lit at room temperature.

So basically, for common liquid hydrocarbons, the main figure is the flash point.

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Just for interest: I did try solid magnesium (not powder), and it's very hard to lit. I had to use oxygen+acetylene for a long time to first melt a part of the ingot, heat it a lot past melting, and at that point I could remove acetylene and burn magnesium in pure oxygen - far less spectacular than polyethylene for instance. Removing oxygen as well, the hot magnesium ingot went on burning in air with a weak pale green flame and could be extinguished by human blow.

Compare with titanium, whose chips readily catch fire when turning or milling, produce extremely hot white flames and ignite just anything they fall on: magnesium flammability is just badly understood.