R. Meyer J. Köhler A. Homburg Explosives

319 Thermodynamic Calculation of Decomposition Reactions
The total mole number n is not altered by the water gas reaction; K1, is
therefore independent of the total pressure p, but depends on the
temperature (W Table 36). Equation (5) can be written as
K1 = n2 ·n4
n1 · n5
The reaction for NO formation must also be considered
1/2 N2+CO2 = CO+NO
with the equilibrium equation
K2 =
[CO] · [NO]
[N2] 1/2 · [CO2] =
K2 = öä p
n
n4 · n6
öäääää
n3 · n1
p
n n4 · p
n n6
( p
n) 1/2 · n3 1/2 · p
n n1
or
(5a)
K2: equilibrium constant,
p: total pressure; p/n-n1, etc., the partial pressures
n: total number of moles
Because NO formation involves an alteration of n, the equilibrium
constant K2 depends not only on the temperature, but also on the total
pressure p.
For the calculation of the six unknown mol numbers n1 ... n6, there are
six equations. Alteration of the mole numbers cause alteration of the
values for the reaction heat, the reaction temperature, the reaction
pressure, and hence the constants K1 and K2. Calculations without the
aid of a computer must assume various reaction temperatures to solve
the equation system, until the values for the reaction heat as a
difference of the energies of formation and the internal energy of the
reaction products are the same (as shown above for the detonation of
industrial explosives). This is a long trial and error calculation; therefore
the use of computer programs is much more convenient.
For low caloric propellants and for highly negative balanced explosives,
such as TNT, the formation of element carbon must be assumed
(Boudouard equilibrium):
CO2+C = 2 CO
with the equilibrium equation
K3 = [CO]2
[CO2]
Explosion fumes with a dark color indicate the formation of carbon.
The calculation becomes more complicated, if dissociation processes
(6)
(7)