1 Q about Flammability

This can be explain by the concept of "intermolecular force"

For simple structure, molecules are held together by weak van der Waals' force, the strength of the attraction force depends on the size and shape of the molecules

For larger number of hydrocarbon molecules, the number of atom in one molecule is more, and the size is larger. Therefore, the van der Waals' forces is stronger than those hydrocarbon molecules with less number of atoms in one molecule.

For stronger van der Waals' forces, it will require more energy to break down the bonds, and the attraction forces, i.e. the boiling point and melting point is higher for larger number of hydrocarbon molecule.

Maybe I can reask this Q later?

Up to this moment no one can point out "why smaller intermolecular force / lower b.p. would lead to higher flammability".
Also, 003, what bonds are you breaking? covalent bonds or intermolecular attraction?

2012-04-13 10:29:42 補充：
I'm willing to do so if I can; yet right now I don't have some free time.... So now I can just put up some short discussion & thinkings.

002 has the point. Smaller hydrocarbon molecules have lower molecular size, so they have weaker van der Waals' forces. This explains why smaller hydrocarbons have low boiling point. And small amount of heat energy is sufficient to ignite them.

2012-04-09 23:45:16 補充：
All in all, the intermolecular forces between hydrocarbons with low no. of carbon atoms are weaker than those between hydrocarbons with high no. of carbon atoms --> small amount of heat energy is required to break the intermolecular forces between the low one rather than high one.

2012-04-09 23:48:13 補充：
Well, if you have more in-depth discussion on the topic, why don't you answer it? Glad to hear if you can answer it.

Refer to the fractional distillation.
The boiling point of LPG is 2X degree Celsius.
But the boiling point of diesel is about 300 degree Celsius.
That means that LPG needs a lower temperature to burn.sothe flammability of smaller hydrocarbon molecules (e.g. LPG) is higher
than that of the larger hydrocarbon molecules

This is because smaller hydrocarbon molecules is easier for burning since their structures are simpler than that of larger hydrocarbon molecules.Therefore,their boiling points are also lower that they can provide energy faster.