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Chemistry > Explosives > Flashcards

Explosives Flashcards

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1
Q

What is an explosion

A

Sudden release of large amounts of energy

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2
Q

what separates an explosion from burning

A

rate at which energy is released

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3
Q

What is a nuclear explosion

A

energy released from fragmentation of unstable nuclei

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4
Q

What is a physical explosion

A

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

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5
Q

What is a chemical explosion

A

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.

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6
Q

What does a chemical explosive contain

A

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

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7
Q

Why is high N content desirable

A

Leads to nitrogen gas

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8
Q

Describe properties of the explosive RDX

A

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

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9
Q

What is the enthalpy of explosion or heat of detonation

A

Heat generated from an explosion

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10
Q

What is the driving force for most explosions

A

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

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11
Q

Comment on the entropy of explosives

A

positive hence Gibbs free energy is highly negative

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12
Q

What is the importance of Nitro groups

A

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

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13
Q

What is black powder

A

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.

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14
Q

What is gun powder

A

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

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15
Q

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

A

As it is more powerful and detonates even when unconfined.

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16
Q

How is NG made

A

Glycerol + Conc nitric and sulphuric acid.

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17
Q

What is the mechanism

A

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

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18
Q

Describe the properties of NG

A

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.

19
Q

How do you calculate oxygen balance

A

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

use Mr

20
Q

What is a problem associated with NG

A

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

21
Q

what is dynamite

A

NG absorbed into keiselghur to form a paste

22
Q

what do you know about nitro cellulose

A

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

23
Q

what is gun cotton

A

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

24
Q

What do you know about picric acid

A

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

25
Q

How is PA synthesised

A

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

26
Q

what are some of the properties of TNT

A

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

27
Q

how is TNT prepared

A

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

28
Q

How can TNT be improved

A

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

29
Q

Is TNT safe

A

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

30
Q

what happens in a low explosive

A

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

31
Q

what happens in a high explosive

A

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.

32
Q

How to do you work out the Power index

A

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

33
Q

How is Q and V calculated for the explosive

A 
Q = Enthalpy / Mr 
V= volume of gases used using the ideal gas eqaution.
34
Q

How does Al improve TNT

A

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

35
Q

What are the properties of nitro based explosives

A

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

36
Q

Why is ammonium nitrate used as a component of explosives mixtures

A

positive oxygen balance. cheap and safe, easily available.

37
Q

Describe properties of HMX

A

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

38
Q

describe properties of octa cubane

A

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

39
Q

What are azides

A

crystalline salts of N3-. highly sensitive

40
Q

why are azides used in airbags

A

heat generated is low and N2 is product which is harmless

41
Q

Describe tetrazene

A

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

42
Q

what is TATP

A

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

43
Q

Why is TATP used so widely

A

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

Chemistry (22 decks)

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