Discuss with references to high and low explosives the ideal features of an explosive reaction, explaining, with examples, how chemical reactions produce energy and how they cause an increase in pressure.
A chemical explosive is a compound or mixture which, upon the application of heat or shock, or rearranges with extreme rapidity, yielding much and heat. . It takes energy to break chemical bonds. And energy is released when new chemical bonds form, this being how the energy is produced. When there is more bond-making than bond-breaking, the excess energy is released, making the surroundings hotter. Low explosives are normally employed as . Most low explosives are mixtures; most high explosives are compounds, but to both there are notable exceptions. High explosives are also called detonating, and low explosives are referred to as burning mixtures. The difference between detonation and burning is that a burning mixture simply burns at a very fast rate, usually not exceeding the speed of sound, needing other methods to produce an explosion. Detonation, on the other hand, occurs almost simultaneously through the whole mass of the mixture.
For something to be explosive it must take place very quickly, it must be an exothermic reaction {heat must be given out} and as many of the products must be gases. In an explosion the gases are hot and are produced quickly in an enclosed small space, like a bullet or shell. This leads to a big rise in pressure which ultimately causes the explosion. {2,4, 3}
{Picture: high explosives are used for mining; the picture shows an explosion taking place in a rock face}{5}
Give an account of the development of chemical compounds for use in explosives. Describe the advantages of each new chemical explosive over its predecessors and describe how the explosives were adapted to make them safer and more effective.
In 1847 an Italian scientist named Ascanio Sobrero mixed together nitric acid, sulphuric acid and glycerine. The new substance he had made was a yellowish oil. He had discovered nitroglycerine and found its behaviour very unpredictable. In 1852 Alfred Nobel started research into making nitroglycerine safe. Nobel made a safe explosive by mixing nitroglycerine with kieselguhr to make a paste. This paste was shaped into rods which could only explode when detonated deliberately. Nobel then went on to develop a safe way to detonate the new dynamite. He used a small explosion from a small amount of gun powder to set off the nitroglycerine. This making the explosive a lot safer. In1867 Nobel realised that a more effective mixture could be made by replacing the inert kieselguhr with a substance which itself would burn or explode. He did this by mixing the nitroglycerine with charcoal, barium nitrate and sulphur. However further development was needed as the performance of the explosive varied. His third invention was by adding 7/8% of collodion to warm nitroglycerine this formed a still jelly like substance which became known as blasting gelatine. This substance was a lot more effective as it proved to be a more powerful and reliable explosive.
C3H5{OH}3 + 3HNO3 C3H5{NO}3 + 3H2O
Glycerine Nitroglycerine
H2C OH Catalyst {concentrated H2SO4} H2C O NO2
HC OH + 3HNO3 HC O NO2 + 3H2O
H2C OH H2C O NO2
{The manufacture of nitroglycerine: by reacting glycerine with concentrated nitric acid.}{3}
The development of high powered explosives did not stop there. Trinitrotoluene was developed during the Second World War. Unlike the old nitroglycerine the new TNT contains nitro groups {NO2} rather than the old nitrate groups -O-NO2. The development of TNT was a great advantage as it melts at 81oC and therefore can be melted and poured into shells and over weapon devices. It also does not react with metal therefore metal bomb containers can be used. {1,2,3}
Discuss how attitudes to health and safety in chemical research and industrial chemistry have changed over time. Use examples from the history if the development and manufacture of explosives and medicines.
In the past is seems that all chemists discovered different chemicals but sheer chance. This however proved a very dangerous way of making advances in chemical research. For example: when Alfred Nobel’s research into the properties of nitroglycerine killed his youngest brother and another chemist in an explosion. Similarly when a chemist called Sobero tasted the substance he was researching to see if it was dangerous, this could have killed him. As you can see from the examples health and safety was never really considered. Now attitudes are completely reversed. Health and safety legislation is a massive part of research and development. Governments instate a lot of legislation for the handling and storage of explosives, for example the ‘Occupational Health and Safety Amendment (Dangerous Goods) Act 2003’ and. Everything is thought about from the handling to the transport of chemicals.{3}
h
{Explosive hazard sign. Warns that a substance is explosive in certain circumstances}{5}
References:
Cordite from Conkers – “Conkering Cordite” by Wilson Flood, Chemistry Review, Volume 10, Number 2, November 2000{1}
.{2}
“The Big Bang – a History of Explosives” by GI Brown, which appeared in chemistry review, Volume 9, Number 4, November 1999.{3}
Salters Chemical Ideas – Pg 358{4}
http://en.google.co.uk/images/explosive.{5}
Summery
To summarize oxidation is the addition of oxygen, for something to be explosive it must take place very quickly, it must be an exothermic reaction and as many of the products as possible must be gases. High explosives are also called detonating, and low explosives are referred to as burning mixtures.
