posted November 15, 1999 07:45 AM         

Basicly when chemical elements combine, two types of
equations are useful to pyrotechnics. These are the weight
and heat equations.

Chemical elements are the most basic combinations of
electrical particles which make up the stable matter we can
touch and feel.

The chemical equations for already combined elements, which
are called compounds, are grouped in two families, in
chemistry books, organic and inorganic. Organic are those
containing the element carbon and the inorganic are those
which do not contain carbon.

The way for pyro's to find the proper equations for chemical
compounds, or for elements is to look them up in books.
A good one is the "Handbook of Chemistry and Physics"
published by the Chemical Rubber Publishing Co. It's a very
fat little book, printed on very thin paper pages, and older
editions of it going back 50 years are still useful for in-
organic chemical uses. Most libraries have copies of it. You
can also get them at flea markets or used book stores.

A simple equation is used for illustration:
Zn stands for the element Zinc,
S stands for the element Sulfur
Let us combine these elements to demonstrate the use of the
two types of equations.
The first equation regulates the amount of each element that
must be combined to make things work best. If you have the
wrong amounts you get partial combination, and poor reaction
for pyro uses.
The reaction formula is:
Zn + S = ZnS
Which says one molecule of Zinc + one molecule of Sulfur
combines to form one molecule of Zinc Sulfide. The number of
molecules of each is the same on both sides of the = sign,
so its a good formula. Whether it will actually work must be
tested.

Look up Zinc Sulfide in the "Physical Constants of Inorganic
Compounds" part of the book and it says:

Name,Zinc Sulfide; Formula, ZnS; Mol Wt, 97.45

Do the same for Zinc and for Sulfur: The elements are in the
inorganic section of the book:
Zinc Zn Mol Wt=65.28
Sulfur S Mol Wt=32
(Notice that book lists S8 as the preferred way for sulfur
atoms to clump together, but we are only interested in what
One atom of the element weighs so we divide the 256 mol wt
it lists for 8 S atoms by 8 to get 32 the wt of one. Most
books will list the wt of S as 32 without bothering to
mention it likes to group into bunches of 8. This bunching
is not very important for elements in this formula.) We
could use the S8 just as well and the formula would be
8 Zn + S8 = 8 ZnS which is the same only the quantity is
now 8 times as much as before but the RATIOS are the same,
meaning one Zn for each S.

You can't mix one molecule for its too small, so we use the
formula wt. It's the weight of the compound which contains
10 to the 23 power of molecules or atoms. 32 grams of S
contain the same number of atoms as does 65 grams of Zinc.
This means each Zn atom can find a partner S atom and none
get wasted because they can't find a partner.

So our formula now is Zn + S = ZnS
put the formula weights in 65 + 32= 97
This says weigh 65 grams of zinc (as a powder usually)
and mix it with 32 grams of Sulfur( as a powder usually)
Mix well, and if ignited it will burn to form 97 grams of
Zinc Sulfide (as smoke usually)

The heat of formation formula gives the heat involved: The
heat required to form any compound is listed in that book as
"Heat of formation for compounds".

Zn being an element is not listed because elements have no
heat of formation for they are not compounds yet. Its value
is 0.(This statement is accurate enough for pyros).

S is and element and its heat is 0

ZnS is a compound and its is listed as 45.88 Kilo Cal per
mole wt or formula wt (meaning 45,880 calories per 97 grams
of ZnS compound formed. That is not a negative number so
that amount of heat is created when that compound is formed.
Had the number been negative then that amount of heat would
have been absorbed from the surroundings when it was formed,
and stored in it as a form similar to the energy stored in a
clock spring when it is wound up tight. That stored energy
can be released when a negative compound is again converted
back to elements. On this matter of heats, be aware that
when you find a compound that has large + numbers, like
several hundred calories per gram of mixture, the heat
released is getting explosive, and if over a thousand it can
be a dangerously explosive compound. The infamous armstrong
compound has a number around 1500. It is well known for the
many chemists it has scorched, and blasted apart, when
formed by mixing chlorates with red phosphorus. Large
calorie numbers tend to create so much heat that things "go
off" very quickly, and very violently.

Back to our example:
The formula is:
Zn + S = ZnS
the heats are 0 + 0 = 45 Kcal
so there is no heat on the left and 45,000 on the right so
its all created when these elements burn together.
That amounts to 464 calories per gram which is a lot of heat
and this mixture could be expected to react violently. In
fact is burns about as fast as poorly mixed black powder,
and radiates a lot of heat from the incandescent cloud of
ZnS formed. It is dangerous to light with a match for your
hand will usually get burned from the flare up. It is not
very explosive for all the products are solids. Gasses are
needed to make strong explosions. This is not an explosive
although it makes a helluva fire.

When writing formulas 2 Zn would mean two molecular (or
formula) wts of Zinc, etc.
Some compounds travel as a family unit, like the nitrate
group. Its formula is NO3 meaning one nitrogen atom and 3
oxygen atoms like to stay united and move as a unit unless a
particular mixture causes them to split apart. They split
apart easily, so that group is very useful to make
explosives as they split and give up their oxygen easily.

Such family groups are written in formulas of compounds as
(NO3)2 for example, if 2 such groups must be contained in a
formula. The number AFTER the ( ) tells how many groups are
included in each molecule of that compound.
The number BEFORE the compound tells how many molecules of
the compound must be used to make the formula balanced.
If its not balanced things do not work as fast and some will
be wasted for lack of a partner.

Ca(NO3)2 + 3S = Ca0 + 3S02 + 2N is an example of a compound
that contains two groups of nitrate in each molecule of
calcium nitrate.
Note, Ca(NO3)2 = 1 Ca + 2N +2x3 O atoms. You always end up
with the same number of atoms each side of the equation when
all is balanced and every atom gets a partner in the reacted
result, or it ends up as an element.

The formula says 2 groups of nitrate (NO3) combined with one
atom of Ca, sometime in the past, to make the calcium
nitrate you are using to start with. Lots of heat was given
off when it did that for its heat of formation was 225. That
heat was already lost, and its going to be reabsorbed when
that compound splits back up in this equation. That heat
will be taken from the heat formed by the products on the
right side of the equation. Whats left over is the heat this
reaction will create. More on this later.

In this equation, one molecule of calcium nitrate mixes with
three atoms of sulfur to make one molecule of calcium oxide
(lime) and one molecule of sulfur dioxide, a very stinky
gas, and 2 atoms of Nitrogen gas.

balancing the formula so equal number of elements appear on
both sides of the = sign:

Ca(NO3)2 + 2S = CaO + 2SO2 + 2N + O
That lonely O on the right side can burn some S if I mix a
bit more S into the batch. To find out the right mix I have
to play with the numbers till I get the O used, but still
have the same number of elements on both sides of the =
sign. Much trial and error playing results in this formula:
2 Ca(NO3)2 + 5S = 2CaO + 5SO2 + 4N
On the left there are:
2 Ca and 2x2N and 2x2x3O and on the right there are
2 Ca and 4N and 2+5x2 O and 5 S so it balances

Looking up the formula wts:
Ca(NO3)2=164
S=32
CaO=56
SO2=64
N=14

Putting them in the formula:
2 Ca(NO3)2 + 5S = 2CaO + 5SO2 + 4N
2x164 5x32= 2x56 5x64 4x14
So the right mixture is:
328 grams Ca(NO3)2 mixed with 170 grams S
Note if the formula is right the wts on each side of the =
will be the same.
2x164 gms + 5x32 gms = 2x56 gms + 5x64 gms +4x14 gms
488 =488

Now look up the heats of formation:
Ca(NO3)2 =225
S=0
CaO=151
SO2=75
N=0

Put them in the formula:
2 Ca(NO3)2 + 5S = 2CaO + 5SO2 + 4N
2x225 5x0 2x151 5x75 4x0
all heats on the left of = must be subtracted from all heats
on the right side of =.
450=302 + 375
450=677 which means we get a net excess of heat on the right
side amounting to 677-450= 227 Kcals for an input of 488
grams of stuff so the reaction gave 227/488 or .5 Kcal per
gram, or 500 cal per gramof the mixture, which is a lot.

This mixture could be expected to make a lot of heat, and
might go fast, but you would have to try it to be sure. The
amount of heat warns you to be careful. Nitroglycerine
delivers about 600 calories per gram if my memory serves me
correctly, but I don't have time to look that up now.

The amount of heat formed suggests how fast the reaction may
go but is not the only thing controlling it. Nitroglycerine
goes in microseconds, but the mixture above might take
seconds to go. Test to find out, unless you are acquainted
with very advanced chemistry calculations. Test in SMALL
quantities, so if you are suprised, the surprise will be
physically small.

As an example of a violent reaction which everyone tells you
to be wary of mixing:

KCLO3 = 122 gms/mole = 90 Kcal/mole
P = 31 = 0
P2O5 = 142 = 365
KCl = 75 = 104

10 KClO3 + 12 P = 6 P2O5 + 10 KCl
wts 10x122 12x31 6x142 10x75
1220 gms 372 gms =
heats 10x90 12x0 6x365 10x104
900 0 2190 1040
900 =3230 so there is an excess of 2330 Kcal for
1220+372=1592 grams of mixture or 2330 Kcal/1592 grams, or
1.463Kcal/gm or 1463 calories per gram, which is a hell of a
lot of heat, so expect this mixture to be dangerous. In fact
it's famous for its dangerous nature.

It has burned almost every person who fooled with it. The
reason it's so dangerous is that phosphorus is almost ready
to spontaneously combust at room temperatures. Its molecules
are already vibrating so violently that they are near the
impact velocity needed to react with most other element near
them, and chlorates are also vibrating so violently they can
give up oxygen to anything rather easily. The combination is
a recipe for disaster.

If you were mixing it at 300 degrees below 0 F it would be
as tame as other compounds we mix. Sulfur is a bit farther
than is phosphorus from its reaction temperature at normal
room temps, but it's close enough to make sulfur/chlorate
mixtures quite touchy. Both sulfur and phosphorus slowly
react with oxygen in air, and the oxides absorb moisture
from the air, to make acid which GREATLY increases the rate
of oxidation as the chlorate then begins to give off its
oxygen more easily.

Such mixtures must have a small amount of basic material
added to them to neutralize the acid to make them storeable
at all. Chalk, or soda or some other easily decomposed
carbonate is usually used to get rid of the acid as it
forms. Many pyro mixtures call for carbonates to keep acids
neutralized. About 1% of the mix wt of carbonate is added to
stabilize it. Both mistures are sensitive to friction.

The P mix is so sensitive you will get burned by it usually
if you handle it at all roughly. Grinding it always explodes
it. Sulfur mixes are less touchy, but won't tolerate
grinding. Both are sensitive to blows, and to flames or
sparks. They are considered too touchy to use, by
experienced pyros.

The only commercial use for chlorate sulfur mixtures I can
recall was the old railroad torpedoes that were put far down
the tracks from danger to warn approaching trains. They were
made from chlorate sulfur mixes that exploded with a roar
when metal train wheels ran over them. They had additives to
keep them safe for normal handling.

In the vietnam war American military idiots made chlorate
phosphorus filled pouches and stored them in freon tanks and
dropped them on jungles so anything walking on them after
the freon evaporated exploded them. They would take off an
animal's foot, and were used to warn our listening devices
that something was walking around along trails used by enemy
troops. Some test dropped in the ocean in Florida, washed
ashore on a public beach. A soldier sent to pick them up was
killed when he threw a box of them on his truck. They had
dried out enough on the beach from both the water and the
freon, to go off. When one went the whole box went, and he
also went.