1.Oxidation is when a substance gains oxygen, lose

s electrons, and itsoxidation state increases after a reaction.

One example of an oxidation reaction is:
C + O2CO2
(s)(g)(g)
In this reaction, the carbon has become oxidised (gained oxygen) and its
oxidation state has changed from 0 to +4.

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Explosive reactions are oxidation reactions that happen very quickly and
exothermically, and where more gases are released to cause greater
pressure, and thus an explosion.

An example of this is the ignition of black powder:
KNO3 + 3C + SK2S + N2 + 3CO2
(s)(s)(s)(s)(g)(g)
Source 1
In this reaction, The C and S are fuels and the KNO3 is an oxidiser. The
products are mainly gases, which cause an increase in pressure. The
reaction happens quickly because there is oxygen contained in the reactant
KNO3, this means the oxygen is available immediately, which allows the C
and S to burn extremely quickly.

The extent of explosive reactions depend on the speed of the reaction,
energy released, and amount of pressure created due to the production of
gases.


2. The earliest explosive is believed to have been invented in China
centuries ago. This was named black powder which is composed of compressed
potassium nitrate, Sulphur and Charcoal. This was used for centuries for
fireworks and warfare.

One problem with it being used in warfare was that the explosion produced a
lot of smoke, which obscured sight. In battles where there was extensive
use of black powder (or gun powder when used in guns as a propellant) the
grounds were covered in smoky fog.

Nitrocellulose (or Gun cotton) was accidentally discovered by Dr Christian
Schnbein in 1846 when he was experimenting with acids at home. His
discovery led to the research of Nitrocellulose in the 1860s for use in
warfare.

A year later, Ascanio Sobrero was also experimenting with concentrated
acids, mixing nitric and sulphuric acid together, along with glycerine (a
more chemically accurate name is glycerol as it was later discovered to be
an alcohol).

He found that this yellow oil was a very unpredictable explosive that could
be detonated by the touch of a feather. This new explosive was named
Nitroglycerine.

Later, a scientist called Alfred Nobel continued Sobrero’s research, making
Nitroglycerine safe by mixing it with Kieselguhr (a silica-based mineral,
similar to clay). The resulting paste was shaped into rods to form sticks
of dynamite which would only detonate when intended. Nobel had invented the
first safe high explosive. This explosive was difficult to detonate with
fire or a fuse, and so Nobel used a smaller explosion to detonate the
Dynamite. He used small amounts of black powder to do this.

This was later made more effective by replacing the Kieselguhr with
substances that had similar properties but would themselves burn or
explode. This was called Dynamite no.2. He later thought of using
collodion, partially nitrated cellulose, instead of fully nitrated
cellulose. The result was a stiff jelly-like mass called blasting jelly,
which was more effective than dynamite, for both the nitroglycerine and the
collodion were explosive.


By the 20th century, black powder used in guns was replaced by smokeless
powder made from Nitrocellulose. Unlike black powder, this explosive could
be detonated by percussion, therefore a fuse was unnecessary.

The British army developed smokeless powder called cordite in the 1880s,
made from Cellulose trinitrate and glycerol trinitrate.

The end product is not in fact an explosive, but merely a very rapid
ignition that creates pressure from the produced gases.

Source 2
During the second world war, TNT (trinitrotoluene) was developed, which has
NO2 nitro groups and not -O-NO2. Because it does not react with metals and
has a melting point of 81oc, it could be poured into metal artillery shells
and bombs.


3. For a reaction to be explosive, it must happen extremely quickly, it
must be exothermic (heat discharged), and gases must be produced.


The reaction can happen quickly because the oxygen source is contained
within the reactants. This is because the oxygen is available immediately.

The more oxygen available, that faster the reaction can happen.

For the reaction to be exothermic, bonds in the molecules must be broken,
causing heat energy to be released. How much energy released depends on the
bond enthalpies between each atom.

For example the N-O bond has an enthalpy of +214kJ mol-1, the N=O has
+587kJ mol-1.

When hot gases are produced in a confined space there is a big rise in
pressure. When this happens very quickly, it can be called an explosion.


Nitroglycerine
C3H5N3O93CO2 + 21/2H2O + 11/2N2 + 1/2O2
(l)(g) (g)
(g)(g)
1 mol of liquid 7.25 mols of gas
This equation shows how 1mol of Nitroglycerine, a high explosive, produces
7.25mols of gas, whereas black powder only produces 4mols of gas from 5mol
of reactants:
KNO3 + 3C + SK2S + N2 + 3CO2
(s)(s)(s)(s)(g)(g)
5mol of solid1mol of solid, 4 of gas
4. Propanone was in demand during the first world war and new methods of
production had to be invented. Previously propanone was produced by the dry
distillation of wood excluding air.

In 1914 Chaim Weizman used bacterial fermentation of starch from maize to
produce propanone. Later on, a lack of Maize resulted in the use of conkers
using the same process. This however was less efficient.

Later, propanone was produced by passing propan-2-ol vapours over a copper
catalyst. The source of the propan-2-ol is propene, a result of crude oil
cracking.


5. Safety during the development of these explosives was relatively poor,
as some scientists would experiment in their own homes, despite working
with dangerous and explosive chemicals. There were many accidents,
including that of Nobel’s factory which resulted in the ban of explosive
manufacture near residential areas in Sweden.

Those manufacturing some of these explosives also had illnesses such as ‘NG
head’ where Nitroglycerine was produced.

However, Nitroglycerine can be used beneficially in the treatment of angina
pectoris.

The production of TNT caused headaches, anaemia and skin irritation in the
workers.

Nowadays there are strict regulations enforced by the Healthy and Safety
Executive, which provides detailed information on dangers of explosives and
protection of workers against chemical effects.

Source 3

___________
Sources:
1. http://www.madsci.org/posts/archives/sep99/937019405.Ch.r.html
2. http://www.chuckhawks.com/smokeless_powder.htm
3. http://www.hse.gov.uk/comah/sragcwh/hazards/haz5.htm
‘Salter’s Advanced Chemistry: Chemical Ideas’ book was also used as a
reference.

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Page 1 word count: 454
Page 2 word count: 346
Page 3 word count: 178
Total word count: 978 (excluding equations)
Explosives and their History

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