Long Industrial Report

Alexander Wade Long Industrial ChemistryReport
13/10/2014 alexdragon26@hotmail.com
Long Industrial Report
Chemical Explosives
A Brief Summary:
Contraryto what one wouldexpect,whencomparedtothe energydensitiesof chemicalssuchas
petrolsandBiofuels,chemical explosivesusuallyhave arelativelylow energydensity.Thismeans
that one mole of petrol or a biofuel will releasemore energywhencombustedthanachemical
explosive suchas Trinitrotoluene(TNT).The reasonan explosive’seffectsare somuchmore
catastrophicisdue to the speedatwhichthe energyisreleased. TNTtypicallyexplodesatavelocity
of 6,950ms-1
(metrespersecond),whereaspetrolstendtobe around300-600ms-1
. The pressure
generatedbythe explosion(knownas‘blastpressure’) causesamajoramountof damage to its
surroundings,aswell asthe rapidrelease of all the storedenergywithinthe moleculesof the
explosive chemical.
Chemical Explosivesare compoundsthatwill typicallyreleaseenergyveryquicklyuponthe
applicationof mechanical stressorsuddenimpact,orhightemperatures. Theyrelease alarge
amountof gaseousatomsandthermal energy,knownas‘evolving heat’.
However,explosive chemicalscannotbe definedbythese propertiesalone,assome chemicalsshow
similartendenciesunderconditionsof hightemperature andpressure aswell,ie NOx.Toovercome
thisblurringof the boundarybetweenwhatisandisnot an explosive chemical, ithasbeen
establishedthatanexplosive chemical mustadhere tothe above propertiesaswell asrapidly
expandandsolelyrelease heat.The keyfactor,though,isthatexplosivechemicalsmustcause an
initiationreactionwhentheyexplode.Thatis,the explosionitself setsoff achainof reactionsthat
are eitherpropagated orterminated byothermeansandchemicals.
Includedinthisreportwill be the some of these reactions,the thermodynamicsof the evolutionof
the producedheat,some key andinterestingexplosive chemicals,andthe effectsof the presence of
otherchemicalsinsolidandliquidchemical explosives.Furtherdiscussionincludesthe useful,and
potentiallyuseful,applicationsof these chemicals.
Nitrogen in Chemical Explosives:
Elemental Nitrogenhasbeensaidtobe one of the most chemicallystable (inert) elements,largely
due to the extremelystrongtriple-bondbetweenthe twoNitrogenatoms.Thisbondrequiresalarge
amountof energytobreak,whichiswhyone of the few everyday occurrences of itbeingbrokenis
inthe enginesof vehicles, wherebothtemperature andpressure are atveryhighlevels.
Despite this,whenNitrogenisbondedasa single atomtoa numberof molecules,forming
compoundssuchas Nitric acid andamines,itschemical andphysical propertiesaltergreatly.Thishas
beenattributedtocertainalterationswithinthe atom;its valenceelectrons are of an odd number
(makingitextremelyunstable,itisa radical),itsoxidisingabilityincreasesdramatically,anditisina
veryunstable high-energystate –lookingtoform three covalentbondsasquicklyaspossible sothat
it can stabilise.
However,despite the factthatNitrogenatomsare typicallymuchlessstable wheninmolecules

otherthan N2,there isa clear difference inphysicalpropertiesbetweencompoundssuch asNitric
acid and Nitrogen-containingexplosives.One keydifference inthe moleculesof Nitricacidandan
explosive,suchas Nitroglycerine,isthat, uponcombustion, Nitroglycerinedevelopsalarge amount
of gas foreach mole combusted,whereasNitric aciddoesnot.
Explosivesfavourreactionswithproductsof higherentropythanthe reactants,evolvingintogases
that expandoutwardsrapidly,atmassive pressures,releasinglarge amountsof energyasheat.
The Nitrogen-containingexplosives,suchas Nitroglycerine, alsocontainandabundance of Oxygen
atoms,allowingforacomplete combustionandincreasingtheiroxidisingcapabilities. Nitricacid still
displaysthe strongoxidisingcapabilitiesthatitwouldbe expectedtoshow,althoughitlacksthe
rapidevolutionof gasandexpulsionof large amountsof energyuponreaction.
ThisincreasedinstabilityinNitrogen-containingexplosivesexplainshow the applicationof
mechanical stressorheat,such as that generatedby friction,tendstoinitiate the explosionof the
chemical.
4C3H5N3O9 (l) → 12CO2 (g) + 10H2O(g) + 6N2 (g) + O2 (g)
[Figure 1] Complete combustion of Nitroglycerine.
Thisinitiation and reactionmechanism canalsobe seenthroughthe combustionof Hydrogenatthe
Hindenburg disaster;a large supplyof gaseousHydrogenandOxygenwere available,andthe
applicationof hightemperaturecausedthe spontaneouscombustionof the Blimp.
From thisitcan be pointed-outthata crucial elementinthe successful combustionof chemical
explosivesisexcessoxygen.
TNT, Nitroglycerine, and Azidoazide Azide:
TNT (2,4,6-trinitrotoluene) isa widelyknownchemical explosive. Itismade-upof 3 Nitro groups
bondedtoa single Toluenemolecule,hence itsexplosive properties.The Nitro groupsare found
aroundthe edgesof the molecule,ratherthanbondedateveryatom, andso have a muchgreater
oxidisingabilitythanif theyhadbeen bonded-tocompletely.
[Figure 2] 2,4,6-Trinitrotoluene.

‘’TNTwas firstmade in1863 by a German chemist, Joseph Wilbrand.He wastryingtomake a
dyestuff,and TNTisyellowincolour.Itwasnearly20 yearsbefore itwasdiscoveredtobe an
excellenthighexplosive.’’-Simon Cotton,RSCwebpage.
One of the mostwidelyknownusesof TNTwasinthe miningindustry,toclearcavernsand
sometimesrescue trappedvictimsof collapsedcaverns.One of the mainreasonsitbecame so
popularwasdue to the factthat is wasmuch easiertohandle,andharderto detonate,thanmany
otherexplosives.
However,the explosive failstooxidise all the Carbonswithinitsstructure,of whichthere are many,
uponcombustion – leadingtoa blacksmoke developing;the resultof incompletecombustion.
Nitroglycerine,however,isamuch lessstable compoundthan TNT.DiscoveredbyanItalianscientist
by combiningglycerine toasolutionof concentrated HNO3 andH2SO4 (Nitricand Sulphuricacid),it
explodedinthe scientistsface,scarringhim.Uponcombustion,one mole of Nitroglycerinereacts
withoxygentoform12 molesof CO2,10 molesof H2O,6 molesof N2, and one mole of O2 – all of
whichare inthe gaseousstate.
The compoundhas beendescribedasextremelyunstable,and“liable toexplode withoutwarning,”
unknown author. Itisprone to explodeuponcontactand applicationof mildshock,makingit
extremelyunstable.
However,despite beingdeemedtoodangerousforpractical use byitsdiscoverer,itlaterbecame
the keycomponentof the popularexplosive, Dynamite.MixedwithSilica,the chemical couldbe
moulded intoshapesandbecame muchlesslikelytocombustwithoutdeliberateinitiation (suchas
applicationof large amountsof shock),andbecame knownasa ‘plastic explosive’,andisusedinthe
extremelypractical shaped charges.
[Figure 3] Molecular model and structure of Nitroglycerine.
An advantage ithasover TNT isthat inthe presence of the same atmosphere as TNT,Nitroglycerine
will combustcompletely.
Azidoazideazide,knownasthe mostexplosive chemical yetknown,wasdiscoveredbya teamof
Germanscientistsfundedbythe U.Sgovernment,inanefforttodevelop‘more energetic
compounds’.Itisa perfectexample of the instabilityof Nitrogenatomswhennottriple-bondedto
each other,asits structure consistsof 14 Nitrogensall eitherdouble orsingle-bondedtoeachother,
as shownon the nextpage.

[Figure 4] Azidoazide azide.
Thiscompoundisextremelyunstable,somuchsothat its sensitivityhasnotbeensuccessfully
measured.Evenwhenputina shock-proof,explosive case,inside adark,climate-controlledroom,
Azidoazideazidewill spontaneouslycombust.
Thisis largelydue tothe absolute instabilityof eachNitrogenatomattemptingtoreactto forma
much more stable compound,thusreleasinggargantuanamountsof energyinthe process –
explosivelydecomposing.Noothercompoundhasbeenfoundthatexceedsthisone intermsof
explosivepotential.
Thermodynamics of Thermal Decomposition of TNT
TNT undergoes the following reaction upon explosion:
2C7H5N3O6(s) → 12CO(g) + 3N2(g) + 5H2(g) + 2C(s)
In thisreaction,the Oxygenandoxidantsforthe process are contained within the chemical TNT. As
you can see, the explosion results in the evolution of large amounts of gas – ten times as many
moles of solid TNT.
The huge increase inentropy in this process means that there are many more molecules present in
the system, and that they each contain greater energy than the reactant. This dramatic increase in
energy implies that the molecules have far more kinetic energy, and therefore expand and move
around the system much more freely than when in the solid state.
This then allows us to assume that the reaction is putting work on the surroundings of the system,
and so a change inpressure andvolume of gas mustoccur. If we look at the equation for calculating
work,w = -P∆V, where ∆V is the change in the volume of gas between reactants and products, P is
the pressurein atmospheres,andthenlookatthe TNT equation, w mustbe a positive value as there
isan increase inthe numberof molesof gas fromproducts to reactants. Thisindicatesanincrease in
pressure in the system, and an increase in the volume of gas.

Applications and Other Useful Properties:
As explosivechemicalsare useful ineverydayapplicationssuchasconstructionworksandmining,
theyare heavilyrelieduponforanefficientsociety.Thusly,improvementstothe speedorcontrol or
powerof the chemicalsandtheirexplosionsare highlysought-after.One notable improvementis
the additionof sensitisers,whichare moleculesthatincrease gapsandspace withinthe explosive
chemicalstoaidin theirexplosion byprovidingmore oxygen-richareastooxidise the compounds,
leadingtocomplete combustion.Ithasalsobeenfoundthatimpuritiesonthe surfacesof the
explosivescanalterthe temperaturesatwhichexplosionsare activated.Theiractivationenthalpies
become dependentuponthe meltingpointsof the impurities,andsoit can be possible tomake very
unstable chemical explosivesstable bystudyingthese effectsfurther;forexample usinganimpurity
witha highmeltingpointtoensure the activationenthalpyof the explosionisatthat highmelting
point–such as the use of clay to stabiliseNitroglycerineinDynamite.
Furtherimprovementsare manyandequallyuseful,suchastimedchargesandsurfactants.
One importantissue withthese explosivesisthattheyare veryharmful and the reactionsare very
fastand hard to control.Thisresultsindifficultywhenmeasuringthe energyreleasedfromdifferent
explosive chemicals,whichtherefore gave rise tomethodssuchasthe Bomb Calorimeter.
It extremelyimportantforchemiststounderstandthese propertiessothattheymaysafely,and
accurately,developthe chemicalsfurther.
References:
1) Nitroglycerine, unknown author,
http://www.chm.bris.ac.uk/webprojects2006/Macgee/Web%20Project/nitroglycerin.htm
2) Chemistryinitselement:compounds,S. Cotton,
http://www.rsc.org/chemistryworld/podcast/CIIEcompounds/transcripts/TNT.asp
3) Chemdraw,2011.
4) 5 of the World'sMost DangerousChemicals, H.Green,
https://www.youtube.com/watch?v=ckSoDW2-wrc

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