TUTORIAL 7 - Chemistry of Explosives (Gases)
1) Explain the following expression:
“Explosions are both enthalpy-driven and entropy-driven. "
2) Ammonium nitrate may also decompose explosively, as in the famous
Texas City disaster of 1947 in which a ship loaded with NH4NO3 fertilizer
exploded. The detonation of ammonium nitrate may be shown as:
2NH4NO3(s)  2N2(g) + O2(g) + 4H2O(g)
How many total litres of gases would be formed by the explosive
decomposition of 454 g of ammonium nitrate at 819oC and 640 torr?
[2.11x103 L]
3) The explosive properties of dynamite and nitroglycerine are due partly to
the large energy change associated with the decomposition of the nitrate
esters, but more important is the large volume change resulting from the
formation of gaseous products. Such a volume change, occurring at a
very rapid rate, in any confined space produces an enormous sudden
pressure. The explosive decomposition of nitroglycerine is approximated
by:
4C3H5(NO3)3(l)  12CO2(g) + 10H2O(g) + 6N2(g) + O2(g)
The energy released by the explosion of relatively small amounts of this
compound may produce temperatures as high as 3000°C. What change
in volume would result from the explosive decomposition of 1.00 litre of
liquid nitroglycerine (density 1.59 g.mI-1) to produce gaseous products at
2500°C in an open field where the atmospheric pressure was 700 torr?
[1.25x104 L]
4) What pressure, in torr, would result if the decomposition of 1.00 litre of
liquid nitroglycerine occurred in a closed room having a volume of 300 m 3
(with original room air at 25°C and 700 torr), with the gaseous products at
2500°C? (Assume that room air was also heated to 2500°C.)
[6.54x103 torr]
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5) Pentaerythritol tetranitrate (PETN) is an explosive used in making
“shaped charges", as in the World War II antitank grenades. When the
compound is formed with a binder into a cone, its detonation
characteristics are such as to direct most of the explosive force towards
the base of the cone. Product temperatures of several thousand degrees,
coupled with an enormous volume change (each mole of PETN releases
2 moles CO, 3 moles CO2, 2 moles N2 and 4 moles H2O(g)), result in a
very high explosive force. What total gas volume at 3000 oC and 800 torr
would result from the detonation of 454 g of PETN [C(CH2ONO2)4]?
[4.05x103 L]
6) Calculate approximate enthalpies of explosion (using bond-dissociation
enthalpy data given below) for:
a)
PETN
[-7.49 kJ/g]
b)
Nitroglycerine
[-7.51 kJ/g]
Compare the answers to the data in Table 2. Account for any differences.
Table 1: Single bond dissociation enthalpies (kJ.mol-1)
C
C
H
N
O
350
415
305
360
435
390
464
160
165
H
N
O
140
Table 2: Double and triple bond dissociation enthalpies
Bond
Bond Enthalpy/
Bond
kJ.mol-1
Bond Enthalpy/
kJ.mol-1
C=C
611
CN
891
CC
837
N=N
418
C=O
745
NN
946
CO
1075
N=O
594
C=N
615
O=O
498
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Table 3: Heat s of explosion of some explosives (in kJ/g)
Nitroglycerine
6.77
TNT
4.56
PETN
6.40
Nitrocellulose
4.41
The molecular structures of some explosives
1 – Nitroglycerine (explosive in dynamite)
2 – PETN (Pentaerythritol tetranitrate)
3 – TNT (trinitrotoluene)
4 - Nitrocellulose (gun cotton)
1
2
4
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