_ [-104.4 + 4(-143.8)] - [-103.4 + 4(0)]
_ -576.2 kcal/mole KC10,,
_ -2.44 kcal/gram of stoichiometric mixture (obtained by dividing -576.2 kcal by 138.6 + 97.2 = 235.8
grams of starting material).
of 2.0 moles (54.0 grams) of aluminum with oxygen gas (48.0
grams) to form A1 20 3 (1.0 mole, 102.0 grams) will liberate 400.5
xampe :
kcal of heat - a sizeable amount! Also, to decompose 102.0 grams Reaction
4 KNO
of A1
3
+ 5 C - 2 K 20
+ 2 N 2 +5CO 2
20 3 into 54.0 grams of aluminum metal and 48.0 grams of oxy-Grams
404.4
60
188.4
56
220
gen gas, one must put 400.5 kcal of heat into the system - an Heat of formation
4(-118.2)
5(0)
2(-86.4)
2(0)
5(-94.1)
amount equal in magnitude but opposite in sign from the heat of (kcal/mole x # of moles)
formation.
The heat of formation of any element in its standard state at 25°C will therefore be 0 using this system.
AH(reaction) = EAHf(products) - EAHf(reactants) A chemical reaction can be considered to occur in two steps:
= [ 2(-86.4) + 0 + 5(-94.1)] - [4(-118.2) + 5(0)]
= -643.3 - (-472.8)
1.
Decomposition of the starting materials into their constitu-
= -170.5 kcal/equation as written (4 moles KNO 3) ent elements, followed by
= -42.6 kcal/mole KNO 3
2.
Subsequent reaction of these elements to form the desired _ -0.37 kcal/gram of stoichiometric mixture (-170.5
products.
kcal per 464.4 grams)
Basic Chemical Principles 27
26
Chemistry of Pyrotechnics
TABLE 2. 7 Standard Heats of Formation at 25°C
TABLE 2.7 (continued)
L Hformation
o H form ation
Compound
Formula
(kcal /mole )a
Compound
Formula
(kcal /mole) a
REACTION PRODUCTS
OXIDIZERS
Aluminum oxide
A1 2 0 3
-400.5
Ammonium nitrate
NH,,NO 3
-87.4
Barium oxide
BaO
-133.4
Ammonium perchlorate
NH 4ClO,,
-70.58
.
Boron oxide
B 20 3
-304.2
Barium chlorate (hydrate)
Ba(C1O 3 ) 2 H 20
-184.4
Carbon dioxide
CO 2
-94.1
Barium chromate
BaCr0 4
-345.6
Carbon monoxide
CO
-26.4
Barium nitrate
Ba(NO 3 ) 2
-237.1
Chromium oxide
Cr 2O 3
-272.4
Barium peroxide
Ba0 2
-151.6
Lead oxide (Litharge)
PbO
-51.5
Iron oxide
Fe 2O 3
-197.0
Magnesium oxide
MgO
-143.8
Iron oxide
Fe 3 O 4
-267.3
Nitrogen
N 2
0
Lead chromate
PbCr0 4
- 217. 7b
Phosphoric acid
H 3PO4
-305.7
Lead oxide (red lead)
Pb 30 4
-171.7
Potassium carbonate
K 2 CO 3
-275.1
Lead peroxide
PbO 2
-66.3
Potassium chloride
KC1
-104.4
Potassium chlorate
KC10 3
-95.1
Potassium oxide
K ,O
-86.4
Potassium nitrate
KNO 3
-118.2
Potassium sulfide
K ,S
-91.0
Potassium perchlorate
KC1O 4
-103.4
Silicon dioxide
Si02
-215.9
Sodium nitrate
NaNO 3
-111.8
Sodium chloride
NaCl
-98.3
Strontium nitrate
Sr(NO 3 ) 2
-233.8
Sodium oxide
N a.0
-99.0
Strontium oxide
SrO
-141.5
FUELS
Titanium dioxide
TiO 2
-225
Elements
Water
H ,O
-68.3
Zinc chloride
ZnC1 2
-99.2
Aluminum
Al
0
Boron
B
0
a
Iron
Fe
0
Reference 1.
Magnesium
Mg
0
bReference 4.
Phosphorus (red)