Explosives

Question 1

What is an explosion

Answer 1

Sudden release of large amounts of energy

Question 2

what separates an explosion from burning

Answer 2

rate at which energy is released

Question 3

What is a nuclear explosion

Answer 3

energy released from fragmentation of unstable nuclei

Question 4

What is a physical explosion

Answer 4

sudden release of pressure (perfect gas law is used for any calculations)

Question 5

What is a chemical explosion

Answer 5

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.

Question 6

What does a chemical explosive contain

Answer 6

Both fuel components (C and H) and the oxidant component (O) in the form of nitro groups.

Question 7

Why is high N content desirable

Answer 7

Leads to nitrogen gas

Question 8

Describe properties of the explosive RDX

Answer 8

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

Question 9

What is the enthalpy of explosion or heat of detonation

Answer 9

Heat generated from an explosion

Question 10

What is the driving force for most explosions

Answer 10

The conversion of molecules with weak bonds to ones with stronger bonds. This is why enthalpy is highly exothermic.

Question 11

Comment on the entropy of explosives

Answer 11

positive hence Gibbs free energy is highly negative

Question 12

What is the importance of Nitro groups

Answer 12

provide O atoms so can convert C and H to CO,CO2 and H20.

Question 13

What is black powder

Answer 13

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.

Question 14

What is gun powder

Answer 14

is a propellant or low explosive. Combustion is slow a depends of the speed of flame. However if confined it will detonate.

Question 15

Why is NG (nitro glycerine) better than black powder for mining

Answer 15

As it is more powerful and detonates even when unconfined.

Question 16

How is NG made

Answer 16

Glycerol + Conc nitric and sulphuric acid.

Question 17

What is the mechanism

Answer 17

Nucleophillic attack of alcohol groups on protonated acid. Water is expelled.

Question 18

Describe the properties of NG

Answer 18

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.

Question 19

How do you calculate oxygen balance

Answer 19

-100 x Mass of extra 02 required/ Mass of explosive

use Mr

Question 20

What is a problem associated with NG

Answer 20

Extremely shock sensitive so needs to be used near to where it was made

Question 21

what is dynamite

Answer 21

NG absorbed into keiselghur to form a paste

Question 22

what do you know about nitro cellulose

Answer 22

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

Question 23

what is gun cotton

Answer 23

is a low explosive and used as a propellant. produced 6 x more gas than gun powder and leaves no residue

Question 24

What do you know about picric acid

Answer 24

is unstable- acid reacts with metal shell to give metal picrate salts. High temp needed to melt moulds

Question 25

How is PA synthesised

Answer 25

Aromatic nitration of phenol via electrophilic attack on aromatic ring using mixture of HNO3 and H2SO4

Question 26

what are some of the properties of TNT

Answer 26

hard to detonate. burns in air. ignition temp is 300. slightly weaker explosive than PA and NG because of high negative O balance -74%

Question 27

how is TNT prepared

Answer 27

Nitration of toluene. requires a stronger nitration mixture as CH3 group is weakly activating.

Question 28

How can TNT be improved

Answer 28

by ammonium nitrate to from amatol. ammonium nitrate is an explosive and improves the detonation.

Question 29

Is TNT safe

Answer 29

yes safe to use as is insensitive to shock, friction and heat.

Question 30

what happens in a low explosive

Answer 30

propagates thermally and slowly. leas to rapid burning which increases with pressure

Question 31

what happens in a high explosive

Answer 31

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.

Question 32

How to do you work out the Power index

Answer 32

Q(explosive) x V(explosive) / Q(picric acid) x V(picric acid)

Question 33

How is Q and V calculated for the explosive

Answer 33

``` Q = Enthalpy / Mr V= volume of gases used using the ideal gas eqaution. ```

Question 34

How does Al improve TNT

Answer 34

Oxidation of Al is exothermic. scavenge oxygen from gaseous products increasing the enthalpy of detonation,

Question 35

What are the properties of nitro based explosives

Answer 35

Multiply Nitro groups. Enthalpically and entropically favourable, weak single N bonds to strong N bonds.

Question 36

Why is ammonium nitrate used as a component of explosives mixtures

Answer 36

positive oxygen balance. cheap and safe, easily available.

Question 37

Describe properties of HMX

Answer 37

lots of nitro groups connected to N. Powerful and safe to manipulate. heat resistant.

Question 38

describe properties of octa cubane

Answer 38

O balance is zero, 12 moles of gas generated. bonds are strained so v exothermic. heat resistant.

Question 39

What are azides

Answer 39

crystalline salts of N3-. highly sensitive

Question 40

why are azides used in airbags

Answer 40

heat generated is low and N2 is product which is harmless

Question 41

Describe tetrazene

Answer 41

Very rich in N which all have weak single bonds. Complete combustion. high shock sensitivity

Question 42

what is TATP

Answer 42

3 eqv of acetone. weak O bonds are reactive. sensitive to friction and heat. Not exothermic, driving force is entropy.

Question 43

Why is TATP used so widely

Answer 43

prepared cheaply and easily and doesn`t involve heat or purification.