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An almighty blasting misunderstanding

I did an ego search to see who was citing my blog; I discovered that one person was using the fact that a chocolate bar contains more energy per kilo as a justification of the inclusion of chocolate in the list of items and materials, which the Israelis prohibit from being imported into the Garza Strip. Now before we get started I want to make it clear that I do not want to get involved in a discussion of the rights and wrongs of the PLO, Hamas, Israeli foreign policy or the Middle East. I want to concentrate on the science of chocolate and bombs, or maybe more correctly the lack of connection between chocolate and bombs.

Now I am a synthetic chemist, it is my job to know how to convert one substance into another. Over the years, I have earned a living often by doing just that. I am well aware that large chemical companies turn air, oil, water stones and salt into a range of products which most people in society think of as ‘plastics’, ‘medicines’, petrol (car fuel), paint, clothing (specialised plastics like polyester [PET], nylon, Kevlar), rubbers and sometimes explosives.

However, I was shocked when one young lady used my blog to justify a ban on supplying chocolate to the Garza Strip (http://answers.yahoo.com/question/index?qid=20100602221408AA9hKfm). This young lady wrote “All the elements needed to make TNT are present in chocolate”.

Let us dissect and consider this statement at length.

Chocolate is mostly sugar (carbohydrate) and fat (lipids) with a small amount of other chemicals such as theobromine. The theobromine is the reason why you must not allow your dog to eat chocolate. I have had one big scare when my omnivore dog (she is like a dustbin) stole some chocolate at Christmas time in 2007.[1]

 Let us go back to our Crunchie chocolate bar, if we read the label of the packet we will find it is

69,9 % Carbohydrate

19,1 % Fat

3,6 % Protein 

Now back to bombs and chocolate, a chocolate bar is mostly carbon, hydrogen and oxygen. The protein content is low so the nitrogen content is low. A typical protein contains about 16% nitrogen (http://www.fil-idf.org/WebsiteDocuments/405-2006%20Comprehensive%20review.pdf). So the crunchie bar contains about 0.6 % nitrogen based on the protein content.

TNT is C7H5N3O6 which is 18.5 % nitrogen, while RDX is C3H6N6O6 which is more nitrogen rich at 38 % nitrogen by weight.

Most explosives are nitrogen rich materials so instantly the woman is wrong in making the claim that chocolate contains all the elements required to make ‘explosives’, when I read explosives I assume she means a typical military or commercial explosive such as TNT, picric acid, RDX or nitroglycerine. The chocolate does not contain the required amount of nitrogen required to make the explosive. Air is 80 % by volume nitrogen so it is important to bear in mind that simple nitrogen content does not allow you to predict how explosive something is.

Next point chocolate contains more energy per kilo than picric acid or TNT, but it is the rate of energy release (power) of the chemical reaction, which is important. My mind turned to a CSE biology book I was given as a young child which explained many details of how plants and animals work to me. I recall reading once that the motto of the parachute school is “knowledge dispels fear”, I would agree with this statement. The book explains why wasps cannot grow to the size of dustbins (Thank goodness !) and it also explains how the amount of energy which a person uses varies greatly as a function of what they are doing. However, the book does give an estimate for roughly how much energy a typical person needs per day. Sadly the book is locked in my basement right now so I had to use another data source.

If we consider an adult using the data on the back of a crunchie packet, the ‘typical’ adult needs 2000 kcal (8409 kJ) per day. Assuming that the adult uses up all the energy and does not put on weight ( Being overweight is a state where you have an excessive energy store) then the power (rate of energy use) is about 97 W.

The man will have an average power of 97 W, if we consider his peak power output using an on-line tool (http://www.pocketdiet.com/calorie_burner_calculator.shtml). If a 75 kg man goes out and shovels snow then each minute he uses up 31.5 kJ. This is a power of 525 W.

Now let us consider a bomb.

A typical small world war two bomb was the German SC50; this contains 25 Kg of TNT (d = 1.654). If we assume that the TNT is in the form of a cylinder (15 cm diameter and 86 cm length), then if the charge is detonated at the centre of one end then as the detonation velocity of TNT is 6850 ms-1 then the charge will require about 125 microseconds to detonate. As the energy of detonation of this explosive charge is 111.9 MJ then the power output of this bomb will be about 90 GW. This is far higher than the man’s power output even if he is fuelled up on energy rich chocolate bars. The important thing here is that the TNT can release its chemical energy more quickly than the sugar in a chocolate bar. Do not let yourself be fooled into thinking that every energy rich material is an explosive.

25 kg of crunchies will have 488,75 MJ of energy in them.


[1] I found my 10 kg food obsessed westie dog with her mouth on the coffee table wolfing down anything within reach. I then asked my wife, where is the chocolate which was in that bowel ? (I thought maybe my wife had moved it). My wife then told me that the dog had got it. I then tried to estimate the chocolate intake that the dog had ingested. It was a lot of chocolate, so I was nervous about her health. I was feeling the dog looking for the first sign of chocolate poisoning (No sign of rapid heartbeat), the dog was excited (but she often is). I later discovered the next day that she had stuffed chocolate inside the sofa for later consumption, so she had only eaten a small percentage of what she grabbed.

 

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One Response

  1. Hiya,

    I like your posting, I’m also amused that the web page quoting you has been taken away… the link is no good anymore!

    My dog has eaten plenty of chocolate before… especially before I knew it was bad for her!

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