What is Flammable Substance?
EdiSon
Why is toluene (b.p 110 ) flammable but water (b.p 100) is not?
What are the factors contributing _flammability_ in a substance?
Is there a term defining the " degree of flammability " for these
flammable substances? If so, how is the "degree of flammability"
determined and ranked?
Perhaps b.p is NOT an important factor?!?
And one last question, what is the most flammable substance known?
Many thanks, E.
Sebastian Hew
news:5c8d8266.01090...@posting.google.com...
> Dear All, if possible, in layman words...
>
> Why is toluene (b.p 110 ) flammable but water (b.p 100) is not?
Boiling point has little, if anything, to do with how inflammable a
substance is, although there is an indirect effect. Boiling point is a rough
measure of how easily a substance is vaporised (although vapour pressure is
arguably a better measure). However, inflammability depends more on the
chemical structure of the substance in question. In general, boiling point
is a function of molecular mass, although there are other factors. For
instance, water has a relatively high b.p. compared to its molecular mass
because of the strong attractive forces between water molecules (hydrogen
bonds). Helium has a b.p. of 4K, yet it is non-flammable.
> What are the factors contributing _flammability_ in a substance?
Suffice it to say that inflammability, in a simplistic view, is a measure of
how much energy is released when the substance combines chemically with an
oxidising agent, e.g., oxygen. For instance, toluene (C6H5CH3) burns in
excess oxygen (O2) to form water (H2O) and carbon dioxide (CO2). Now the
chemical bonds which hold the atoms together to form molecules in toluene
and oxygen gas are weaker, i.e., higher in energy, than those in water and
carbon dioxide, hence energy is given off as heat in the reaction. The
larger the energy difference between the reagents and the products, the more
heat is given off (heat of reaction).
However, it is not enough simply to consider this difference in energy. For
the reaction to proceed, the chemical bonds in the reagents, i.e., toluene
and oxygen, must first be broken so that the atoms can reform into the
product molecules. Energy is required to break these bonds, and the amount
of energy required for this is called the activation energy, which
represents a barrier to the reaction that must first be overcome.
Inflammable substances tend to have lower activation energies for the
combustion reaction, so activation energy is perhaps a better measure of the
inflammability of a substance than heat of reaction, although, keep in mind
that heat generated by the reaction raises the temperature of the system and
promotes further reaction as the activation energy barrier is more easily
overcome.
When I said that b.p. is not measure of how inflammable a substance is, this
is perhaps not entirely true. A combustion can only occur where there is
oxygen in contact with the substance, so inflammability is in part dependent
on the surface area in contact with oxygen. Obviously, if the substance is
gaseous, then oxygen is mixed into the gas providing a situation conducive
to combustion. (Note also that finely divided solids, e.g., aluminium dust,
is much more inflammable than the same solid as a single block.) As b.p. is
related to how easily the substance is vaporised, is it not implausible to
use it as a measure for inflammability. For liquids, the flash point
(generally used of fuels) perhaps provides a better indication than b.p.,
though, because a liquid's flash point is the temperature at which vapour
given off will ignite when an external flame (or other ignition source,
e.g., spark) is applied. Thus, in some senses, flash point is a direct
measure of how inflammable a substance is. Thus, although water has a lower
b.p. than toluene, its flash point is much higher (toluene's flash point
less than 32 deg C, so much so that I'm not sure it makes any sense to talk
about the flash point of water. (Water vapour doesn't burn in air, so flash
point is not a relevant concept.)
> Is there a term defining the " degree of flammability " for these
> flammable substances? If so, how is the "degree of flammability"
> determined and ranked?
A substance is inflammable if it burns in air... this is the simplest
definition. It is perhaps clearer to define a non-flammable substance as one
that does not burn in air, as there are different degrees of inflammability,
which is dependent on factors such as flash point, volatility, boiling
point, surface area, activation energy, heat of reaction, etc. There are
formal hazard rating indices defined for inflammability such as those used
in MSDSs, but I'm not sure what the exact categories are.
> Perhaps b.p is NOT an important factor?!?
> And one last question, what is the most flammable substance known?
I have no idea... in fact, there may not be an answer as I'm not
inflammability is a sufficiently well defined concept. Short of explosives,
though, I would say that ethyl ether probably comes close to being one of
the most inflammable liquids.
>
> Many thanks, E.
Greatest Prime
Hew at rada...@hotmail.com wrote on 9/5/01 8:09 AM:
> Helium has a b.p. of 4K, yet it is non-flammable.
Then why is the US Government spending zillions on and ignition facility?
:=) Oh, I forgot. They are trying to make, not burn helium out of hydrogen.
Bill
Dr. Henry
--
Dr. Henry Boyter, Jr.
Ph.D. Chemist
The opinions of Dr. Boyter are provided for informational
purposes only and should not be used as advice. No
warranty or expression of professionalism is implied.
******************************************************************
"EdiSon" <molub...@hotmail.com> wrote in message
news:5c8d8266.01090...@posting.google.com...
c....@gmx.net
Flamable stuffs are those that easily react with oxygen. Water is
Hydrogen gas that has been oxidized. It can not take up any more oxygen.
To make it happen, the flamable stuff has to get mixed with oxygen.
Roughly speaking: the more volatile the more flamable. Example: light a
candle that has no wick....
Sebastian Hew
<c....@gmx.net> wrote in message news:3B9613C4...@gmx.net...
> > Why is toluene (b.p 110 ) flammable but water (b.p 100) is not?
>
> Flamable stuffs are those that easily react with oxygen. Water is
> Hydrogen gas that has been oxidized. It can not take up any more oxygen.
Hydrogen peroxide, perhaps? Clearly, water is not inflammable, but the point
is not so much that water cannot take up any more oxygen, but rather that to
do so would entail an increase in energy.
> To make it happen, the flamable stuff has to get mixed with oxygen.
> Roughly speaking: the more volatile the more flamable. Example: light a
> candle that has no wick....
I don't see the relevance of the presence or absence of a wick to
volatility.
Greatest Prime
on 9/5/01 5:00 AM:
> Flamable stuffs are those that easily react with oxygen. Water is
> Hydrogen gas that has been oxidized. It can not take up any more oxygen.
What is hydrogen peroxide?
Doron form Israel
is referd as flammable.
Dr Ivan D. Reid
wrote in <B7BD0823.4297%Fish...@mediaone.net>:
>What is hydrogen peroxide?
I thought the same thing. But I rather expect it's not produced
by burning water -- in the same way that I recently decided that there was
no way of producing explosively unstable selenium nitride when melting
pure selenium in a nitrogen-flow cryostat/oven. The fact that PSI is
still intact seems to have validated my decision...
--
Ivan Reid, Physics & Astronomy, University College London. i...@hep.ucl.ac.uk
KotPT -- "for stupidity above and beyond the call of duty".
c....@gmx.net
> volatility.
He was asking for an explanation in layman's terms.
The wick acts as a device for vaporizing the wax. Of course it doesn't make the
wax more volatile, I just consider it a good example for combustion principles.
EdiSon
mentioned... is there any possibility to manipulate these factors to
make water a flammable liquid...~~?
cheers, E.
"Sebastian Hew" <rada...@hotmail.com> wrote in message news:<rerl7.2522>
Colthechemist
> If I'm right a chemical that has an ignition temp. of 60.5 C and above
> is referd as flammable.
point. At 60.5 C & above the substance is regarded as combustible but
not flammable, hence no flammable diamond appears on the label. A
closed cup flash point below 60.5 C means the substance has been
defined as flammable and is classed as dangerous goods which require
special packing & transport.
John Bang
>
> Dear ALL, considering all the possible factors for in_flammability
> mentioned... is there any possibility to manipulate these factors to
> make water a flammable liquid...~~?
Pour lots of petrol into it.
John Spevacek
> mentioned... is there any possibility to manipulate these factors to
> make water a flammable liquid...~~?
Throw in a chunk of sodium metal.
John
--
"Writing is God's way to show you how sloppy your thinking is."
The opinions express in this posting are mine and are not those of my
employer.
Opinions expressed herein are my own and may not represent those of my employer.
Rhonda Moore
rotflmao
rm
Larry Smith
flammability, or inflammability -as the case may be-, by them. These rules
are
standardized to be used as measures of safety in handling and shipping. Get
access to an IMDG, IMCO, or IATA handbook.
The test used in making this determination is the Flash Point, not
flammability or ignition point nor autoignition point, nor a host of other
possibilities.
Confusing matters even more, there are several Flash Point protocols and
apparatus available.
The 'media', as we charitably refer to them, often make a big deal about
'volatility'. They seem to equate volatility with flammability, danger, or
just something indescribable and ugly.
'Volatile' means that it evaporates, more or less quickly. Water is
volatile, so is booze, my bank account, and my tolerance, at times.