Explosives Flashcards
What is an explosion
Sudden release of large amounts of energy
what separates an explosion from burning
rate at which energy is released
What is a nuclear explosion
energy released from fragmentation of unstable nuclei
What is a physical explosion
sudden release of pressure (perfect gas law is used for any calculations)
What is a chemical explosion
Result of a chemical reaction. Fast exo reactions generate large amounts of heat and gas in a small space leading to a blast wave of highly compressed gas.
What does a chemical explosive contain
Both fuel components (C and H) and the oxidant component (O) in the form of nitro groups.
Why is high N content desirable
Leads to nitrogen gas
Describe properties of the explosive RDX
Developed in WW2. Combines C and H as a fuel and O as an oxidant. Contains large number of N atoms with weak single bonds. Only gaseous products (9 moles of gas). C is converted to CO
What is the enthalpy of explosion or heat of detonation
Heat generated from an explosion
What is the driving force for most explosions
The conversion of molecules with weak bonds to ones with stronger bonds. This is why enthalpy is highly exothermic.
Comment on the entropy of explosives
positive hence Gibbs free energy is highly negative
What is the importance of Nitro groups
provide O atoms so can convert C and H to CO,CO2 and H20.
What is black powder
Is a mixture of charcoal,sulfur and KNO3.
the equation of combustion is
10KNO3 + 3S + 8C = 2K2CO3 + 6CO2 + 5N2.
other solid products include KNCS, (NH3)2CO3
lots of smoke is produced.
What is gun powder
is a propellant or low explosive. Combustion is slow a depends of the speed of flame. However if confined it will detonate.
Why is NG (nitro glycerine) better than black powder for mining
As it is more powerful and detonates even when unconfined.
How is NG made
Glycerol + Conc nitric and sulphuric acid.
What is the mechanism
Nucleophillic attack of alcohol groups on protonated acid. Water is expelled.
Describe the properties of NG
All products are gaseous. High O content allows oxidation of C and H to give CO2 and H2O. extremely shock sensitive and may give violent detonation.
How do you calculate oxygen balance
-100 x Mass of extra 02 required/ Mass of explosive
use Mr
What is a problem associated with NG
Extremely shock sensitive so needs to be used near to where it was made
what is dynamite
NG absorbed into keiselghur to form a paste
what do you know about nitro cellulose
made from reaction with paper with conc HNO3
cellulose contains lots of OH which can be converted to ONO2 groups. 11 moles of gas generated. negative O balance
burns vigorously and quickly when detonated
what is gun cotton
is a low explosive and used as a propellant. produced 6 x more gas than gun powder and leaves no residue
What do you know about picric acid
is unstable- acid reacts with metal shell to give metal picrate salts. High temp needed to melt moulds
How is PA synthesised
Aromatic nitration of phenol via electrophilic attack on aromatic ring using mixture of HNO3 and H2SO4
what are some of the properties of TNT
hard to detonate. burns in air. ignition temp is 300. slightly weaker explosive than PA and NG because of high negative O balance -74%
how is TNT prepared
Nitration of toluene. requires a stronger nitration mixture as CH3 group is weakly activating.
How can TNT be improved
by ammonium nitrate to from amatol. ammonium nitrate is an explosive and improves the detonation.
Is TNT safe
yes safe to use as is insensitive to shock, friction and heat.
what happens in a low explosive
propagates thermally and slowly. leas to rapid burning which increases with pressure
what happens in a high explosive
sudden local expansion due to heat and gas generation.. violent heating at front of shockwave. Propagation of shock wave is faster than speed of sound.
How to do you work out the Power index
Q(explosive) x V(explosive) / Q(picric acid) x V(picric acid)
How is Q and V calculated for the explosive
Q = Enthalpy / Mr V= volume of gases used using the ideal gas eqaution.
How does Al improve TNT
Oxidation of Al is exothermic. scavenge oxygen from gaseous products increasing the enthalpy of detonation,
What are the properties of nitro based explosives
Multiply Nitro groups. Enthalpically and entropically favourable, weak single N bonds to strong N bonds.
Why is ammonium nitrate used as a component of explosives mixtures
positive oxygen balance. cheap and safe, easily available.
Describe properties of HMX
lots of nitro groups connected to N. Powerful and safe to manipulate. heat resistant.
describe properties of octa cubane
O balance is zero, 12 moles of gas generated. bonds are strained so v exothermic. heat resistant.
What are azides
crystalline salts of N3-. highly sensitive
why are azides used in airbags
heat generated is low and N2 is product which is harmless
Describe tetrazene
Very rich in N which all have weak single bonds. Complete combustion. high shock sensitivity
what is TATP
3 eqv of acetone. weak O bonds are reactive. sensitive to friction and heat. Not exothermic, driving force is entropy.
Why is TATP used so widely
prepared cheaply and easily and doesn`t involve heat or purification.
