Where does all the energy of a stick of dynamite come from?

Discussion in 'Chemistry' started by Magical Realist, Aug 7, 2013.

  1. Magical Realist Valued Senior Member

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    There's far more energy in the stick of dynamite exploding than can be accounted for by a lit match. Where does this energy come from? It is said energy isn't created. So where was the energy before the dynamite exploded? Was it potential energy inside the stick?
     
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  3. Russ_Watters Not a Trump supporter... Valued Senior Member

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    http://en.wikipedia.org/wiki/Chemical_energy

    [wow]
     
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  5. AlexG Like nailing Jello to a tree Valued Senior Member

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    It's in the chemical bonds of the nitroglycerin which the dynamite is made of.
     
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  7. Aqueous Id flat Earth skeptic Valued Senior Member

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    Adding to what these guys said, MR:

    The molecules in nitroglycerin are formed through relatively weak bonds. That is, they will come apart quite easily and release their raw atoms. This is why nitroglycerine is so unstable. It's always just a small dose of energy away from coming apart (breaking its chemical bonds). The raw atoms will react to form carbon dioxide, water and nitrogen (N[sub]2[/sub]) and (O[sub]2[/sub]). These chemicals have strong bonds and will release large amounts of heat when the new bonds form.

    Here's a chemist's explanation.

    Nobel got his dynamite to be stable by introducing diatomaceous earth as an absorbing agent. It prevents the molecules from colliding or absorbing energy from the environment. Nobel allowed workers to sit only on 2-legged stools. This was to prevent them from falling asleep while tending the dangerous mixture.

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  8. Magical Realist Valued Senior Member

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    AHA! Thanks to all!
     
  9. arauca Banned Banned

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    Explosion is based on some sudden change in volume , were come from conversion of nitro glycerine to as it was mentioned N2 + CO2 + H2O
    Nitroglycerine normally is stabilized in alcohol.
     
  10. Aqueous Id flat Earth skeptic Valued Senior Member

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    Yes the explosion is a rapid self-oxidation of the liquid into a hot gas.

    4 C[sub]3[/sub]H[sub]5[/sub](ONO[sub]2[/sub])[sub]3[/sub](l) → 12 CO[sub]2[/sub](g) + 10 H[sub]2[/sub]O(g) + 6 N[sub]2[/sub](g) + O[sub]2[/sub](g)

    That's 29:4 increase in moles before we factor in gas volume expansion, plus I think around 6 MJ of heat.

    That's true for pharmaceutical nitro -- I'm not sure is that applies to the dynamite or not.

    Originally Alfred Noble was able to stabilize it by mixing it with diatomaceous earth, to form a paste. This gives it a physical stability and simplifies the step of loading it into the tubes (sticks).
     
  11. exchemist Valued Senior Member

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    Indeed. May be worth further pointing out that what makes substances like this explosive, rather than just inflammable, is the point about "self-oxidation", i.e. the oxidiser is contained within the molecule rather than being provided from outside, by the oxygen in the air. This enables the reaction to proceed extremely fast - explosively so.
     
  12. arauca Banned Banned

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    Nitroglycerine is nitroglycerine pharmaceutical or dynamite usage , but I think the one in paste might have an initiator ( fulminant )
     
  13. leopold Valued Senior Member

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    you do not "ignite" dynamite with a match.
    dynamite needs a percussive force to explode, a blasting cap.
    nitrogen bonds.
     
  14. exchemist Valued Senior Member

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    ...and oxygen bonds (to carbon and hydrogen)

    AND, let's not forget the phase change: a small amount of liquid turns, practically instantaneously, into gaseous products, occupying a far larger specific volume at NTP.
     
  15. Magical Realist Valued Senior Member

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    Is the energy released from these bonds related to a force? For example, a rock embedded a cliff has a certain force exerted on it called gravity. The energy it exerts by falling and rolling down the hill is stored potentially within it. Is there a similar force acting upon the atoms that unleashes so much energy? Something like the force of attraction between electrons and their nuclei?
     
  16. exchemist Valued Senior Member

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    Yes I think that's right. The bonding electrons are described as inhabiting a potential well and the reduction in enthalpy when such a reaction takes place is a consequence of those bonding electrons finding themselves in deeper potential wells (= stronger bonds) in the reaction products than they occupied in the reactants.
     
  17. Aqueous Id flat Earth skeptic Valued Senior Member

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    Yes indeed. There is the bond energy to deal with, which is huge, plus the huge energy in the pressure that suddenly develops from rapid expansion of the material in its compressed liquid state to its expanded gaseous state. It's this pressure, or shock wave, which conveys force. The amount of force delivered is equal to the pressure caused the dynamite times the area of the thing being demolished.
     
  18. arauca Banned Banned

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    Remember the rock imbedded on a hill is unstable and will reach a higher stability when comes down to a flat plane . As you said on the hill it have a Potential energy. So is your dynamite It needs an initiator ( shock , spark, fire ). Your rock needs a push and it start to roll at that point ( rolling ) is becoming transformed into kinetic energy.
    I am not to sure if the action is on atoms , but I would accept more the instability is on the molecule itself because it have to many oxydizing group per molecule , the same you can see in TNT ( Trinitro toluene ) and other explosives. At the end what happen the molecule becomes rearranged into smaller molecules which are gas molecules at room temperature , as the rearrangement takes place to form more stable molecules , heat is liberated . Now keep in mind One mole of gas occupies 22.4 liters . One mole of Nitroglycerine will occupy 135 cc but there tere several moles of gas produced . So you can see instant changing in volume from 135 cc to perhaps 80 liters of gas , but this conversion is at room temperature , imagine using the equation PV = nRT were temperature is much larger then RT.
     
  19. Aqueous Id flat Earth skeptic Valued Senior Member

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    That's the most important concept I think. And as you know TNT and the more powerful explosives are similar in that they rely on that very low margin of stability in order to do so much damage - the scientists and weapons people who discovered them managed to find chemicals that have more bond energy and higher gas to liquid ratio.

    Another way of speaking of what we mean by instability is that the energy level of the dynamite in the stick is just slightly less than when it's beginning to explode. It's that huge difference in the amount of energy released, as compared to the amount used to start the reaction, which makes it so powerful.

    If I added correctly is was 29:4 which produces 7.24 moles or 162.4 liters of gas. In terms of the volume increase, that 135cc is equivalent to .135 L, so you've expanded 1200:1 in volume. That goes to pressurizing the shock wave. All that for just a little insight into redox reactions. Damn, you chemists are good for something after all.

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    (Yeah blowing things up. . .

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    That's right, add all of that heat to the room temperature case and it does magnify the pressure wave accordingly. Folks: do NOT try this at home. Oh BTW arauca, I was kidding. The rest of us would blow up out garages. You'd be standing there with your pressure vessels and calorimeters or what not and casually enjoying a controlled reaction.
     
  20. Russ_Watters Not a Trump supporter... Valued Senior Member

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    You were closer with your link to gravitational potential energy. Force and energy are two different things. A rock on a cliff has potential energy based on its height and the force of gravity. A chemical bond is electromagnetic and works more like a compressed spring (still a form of potential energy), but is otherwise similar to gravitational potential energy.
     
  21. wellwisher Banned Banned

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    TNT is trinitrotoluene. The (3) nitro aspects of the molecule, provide oxygen, that will burn the toluene aspect of the molecule (in simple terms). To make this molecule you need to add a lot of energy as heat and acid; tightening a chemical spring.

    Once you ignite it, the molecule supplies its own oxygen, allowing a rapid chain reaction. If we burnt just the toluene aspect in air, the oxygen has to diffuse and react against pressure, making it burn slower for less bang. But with oxygen attached, it is a lightning fast burn; boom!
     
  22. Username Registered Senior Member

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    I'll take a wild guess and say its a chain reaction that causes a sequence of spontaneous events.
     

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