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Offline BetaAmyloid

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Volatile Reactions
« on: October 23, 2009, 07:01:42 PM »
I was wondering what causes volatile reactions compared to small, non-observable reactions - is there anything specific that draws a line between the two?

For example, I have always wondered this (which I am sure everyone has thought about an explosion) but what sets apart an "explosion" compared to the non-volatile reaction of say, sodium and chlorine?

Thanks,
The Cancer Curer
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Offline Mitch

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Re: Volatile Reactions
« Reply #1 on: October 24, 2009, 06:16:27 AM »
I like to think of it in terms of the velocity of detonation, which is how quickly the reaction propagates through a material. Anything that propagates faster than 1000 Mps probably makes a decent explosive.

http://en.wikipedia.org/wiki/Explosive_material#Velocity_of_detonation
« Last Edit: October 24, 2009, 05:07:16 PM by Mitch »
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Offline BetaAmyloid

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Re: Volatile Reactions
« Reply #2 on: October 24, 2009, 01:38:02 PM »
Okay, but specifically, at the chemistry level, are there certain elements, compounds, solutions, etc. that cause the velocity of the reaction to be higher than 1000 Mps?

For example, hypothetically (since this is obviously false), hydrogen reacts with oxygen in a way that it causes a volatile creation of water.

Thanks,
The Cancer Curer
Discovery consists of seeing what everybody has seen and thinking what nobody has thought - Albert Szent-Györgyi

Offline renge ishyo

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Re: Volatile Reactions
« Reply #3 on: October 24, 2009, 01:59:35 PM »
The difference in energetics between reactants and the products, the relative amounts of each present, and the amount of energy available to drive the reaction forward all help determine the rate of a reaction (or "velocity" of the reaction as Mitch mentioned) which in turn is a good indicator of "explosivity" ( :larrow: I'm not using this term rigorously). Fast reactions are typically explosive, slow reactions typically are not.

What makes certain elements more "explosive" typically depends on the products being formed. For example, nitrates can be used as explosives because if you supply a large concentration of them with some energy to start things off, they will react to form the triply bonded N2 molecule. This releases a lot of energy which then increases the rate of other nitrate molecules forming nitrogen and so on and so on until the rate is so fast you have an explosion. Other reactions that explode typically are free radical reactions. You get them going by producing a radical that produces more radicals which produce more and so on and so on so that the rate of the reactions increases very quickly leading to an explosion. Nuclear reactions (On topic!) are harmless in small doses, but if you have a large concentration of fission reactions releasing nuetrons that can feed more and more fission reactions this can eventually lead to a huge increase in the rate of the reaction that ultimately results in a fission bomb.

Of course the explosiveness of a reaction depends on the reaction you are discussing. You might think that sodium and chlorine are "non-explosive" (I'm going to use this instead of non-volatile because it makes more sense to me) because they appear to be harmless when the crystal structure of salt breaks apart in water, but looks can be deceiving. If you were to take pure sodium metal and pure chlorine gas and mix them together in a dark room, exposing this mixture to the light to form the salt would cause a violent explosion. It all depends.

Offline Borek

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Re: Volatile Reactions
« Reply #4 on: October 24, 2009, 03:48:29 PM »
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Offline Borek

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Re: Volatile Reactions
« Reply #5 on: October 24, 2009, 03:51:49 PM »
What makes certain elements more "explosive" typically depends on the products being formed.

Not necesarilly, see acetone peroxide.

Quote
If you were to take pure sodium metal and pure chlorine gas and mix them together in a dark room, exposing this mixture to the light to form the salt would cause a violent explosion. It all depends.

Are you sure? I think they don't need light to react, opposed to the hydrogen/chlorine mixture.
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Offline BetaAmyloid

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Re: Volatile Reactions
« Reply #6 on: October 24, 2009, 05:04:49 PM »
Fast reactions are typically explosive, slow reactions typically are not.

What makes certain elements more "explosive" typically depends on the products being formed.

So, I guess what I'm trying to ask is:

What causes fast reactions at the chemistry level - I understand that you said it usually depends on the product being formed, but what takes place during the reaction that causes the formation of the compound to explode? Such as, bond forming, bond breaking, etc.

Thanks,
The Cancer Curer
Discovery consists of seeing what everybody has seen and thinking what nobody has thought - Albert Szent-Györgyi

Offline Mitch

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Re: Volatile Reactions
« Reply #7 on: October 24, 2009, 05:12:30 PM »
renge ishyo: I was not referring to the rate of a reaction. I was referring to the Velocity of detonation which is a characteristic of the material in an exothermic reaction.

The Cancer Guy: Diamond going to graphite is an exothermic process, not all exothermic processes lead to an explosion. How do I know what will be a good explosive? Here is a simple qualifier for explosives made from nitrogen. The ratio of nitrogen oixde (nitro functional groups) to carbon in a compound can be a good qualifier for how explosive a material is. The more nitro groups, the bigger the boom per mole of substance.
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Offline BetaAmyloid

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Re: Volatile Reactions
« Reply #8 on: October 24, 2009, 05:19:51 PM »
Thanks Mitch, let me know if I'm being a pest. I'm not sure if you read my introduction or not, but I'm 17-years-old and trying to write a book on cancer. I'm extremely interested in all of chemistry, but specifically chemistry of oncology. The only way I know of learning is by asking questions or research -- let me know if I am asking too many questions though.

Thanks,
The Cancer Curer
Discovery consists of seeing what everybody has seen and thinking what nobody has thought - Albert Szent-Györgyi

Offline Mitch

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Re: Volatile Reactions
« Reply #9 on: October 24, 2009, 07:46:30 PM »
Questions are wonderful assuming they're not easily googleable.
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Offline 408

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Re: Volatile Reactions
« Reply #10 on: October 24, 2009, 07:47:08 PM »
Explosive compound result from 3 major sources of potential energy, and I am aware some compounds do not fit in these categories nicely, such as metal acetylides.

Ring strain/cage strain: ex octanitrocubane, trinitroazetidine , HNIW
Carbon backbone oxidation: traditional stuff like RDX, TNT
highly positive heats of formation.azotetrazolates, nitrotetrazoles and other high-nitrogen heterocycles.

Basically you are creating a metastable compound, the products of decomposition(in this case, detonation) are of much lower potential energy than the explosive, so the explosion process releases a lot of energy at once.

Detonation only refers to when the decomposition of a material takes place at a speed faster than the speed of sound in that material.

Why this leads to explosion is you initially have lets say, 1.5g of say, free nitrotetrazole, So HCN5O2.  Say to make the math easy it has a density of 1.5g/cm3 (a reasonable density).  This detonates releasing gaseous water, carbon monoxide/dioxide and nitrogen.  By conservation of mass, this 1.5g of gasses are initially confined to the 1mL originally occupied by the explosive.  I can let you do the math to calculate the pressure, but suffice to say, its really really above STP, so they expand, and they do so really dang fast.  This causes the explosion effect.

For example detonation pressures above 20 Gigapascals are common for explosive materials.

Also, pure sodium in pure chlorine is pretty energetic even with low surface area sodium....

The term volatile to describe a reaction is useless.  Volatile refers to the vapour pressure of a material.

Offline BetaAmyloid

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Re: Volatile Reactions
« Reply #11 on: October 24, 2009, 07:54:42 PM »
Yeah, I know Mitch! - That's why I am here.

Thanks 408, I'll have to google some of the terms used in your explanation since I am not highly educated in explosive vocabulary.

Thanks,
The Cancer Curer
Discovery consists of seeing what everybody has seen and thinking what nobody has thought - Albert Szent-Györgyi

Offline renge ishyo

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Re: Volatile Reactions
« Reply #12 on: October 24, 2009, 10:12:14 PM »
Quote
renge ishyo: I was not referring to the rate of a reaction. I was referring to the Velocity of detonation which is a characteristic of the material in an exothermic reaction.

Yeah, I checked out Borek's link. Pretty interesting that they measure the shockwave of an explosion as a measure of the detonation, but I guess this way of doing things omits the chemical knowledge and would seem easier to handle to some. Oh and, just in case I didn't make it clear, you do not want to try the experiment I mentioned with pure sodium and chlorine btw...you probably *can* get it to go even in the dark (in the light, there would be no doubt).

Quote
What causes fast reactions at the chemistry level - I understand that you said it usually depends on the product being formed, but what takes place during the reaction that causes the formation of the compound to explode? Such as, bond forming, bond breaking, etc.

You have an explosion whenever you have a high concentration of energy that is released to surrounding molecules in a short period of time. As this energy is released to surrounding molecules it increases their kinetic energy, and they blast apart from each other to try and compensate for the energy change (pushing away from each other causes the particles to "cool down"). If you slow down the rate of a reaction, even an explosive reaction can be done without violence. Your body does this all the time. When we combust fat for instance we do it gradually in small steps, so there is no quick violent explosion associated with the process. In your car's engine in comparison, the combustion takes place in one big boom; this causes the gas molecules to push out violently against the piston which ultimately moves the car.

Offline 408

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Re: Volatile Reactions
« Reply #13 on: October 24, 2009, 10:29:50 PM »
Pretty interesting that they measure the shockwave of an explosion as a measure of the detonation, but I guess this way of doing things omits the chemical knowledge and would seem easier to handle to some. Oh and, just in case I didn't make it clear, you do not want to try the experiment I mentioned with pure sodium and chlorine btw...you probably *can* get it to go even in the dark (in the light, there would be no doubt).



?
The velocity of detonation is a direct measure of the propagation of the rate of decomposition/detonation of the explosive.  Fiber optic cables are inserted into a length of charge (suitably away from the detonator if the charge is being overdriven(if the V(det) of the primary is greater than V(det) of the secondary) by the primary) and the fiber optics are hooked up to light detection electronics that can record time precisely.  The distance between the cables and the time it takes between each cable to register light is used as a direct means of measuring the detonation velocity of the explosive.  It is not an indirect measure of detonation by measuring the shockwave, you are directly measuring the reaction(detonation) rate in the explosive.

I have done the sodium chlorine reaction, it is not unsafe if small amounts are used. 

Offline BetaAmyloid

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Re: Volatile Reactions
« Reply #14 on: October 24, 2009, 11:10:23 PM »
Oh and, just in case I didn't make it clear, you do not want to try the experiment I mentioned with pure sodium and chlorine btw...you probably *can* get it to go even in the dark (in the light, there would be no doubt).

Yeah, I wasn't planning on it! Chlorine gas isn't a very user-friendly substance.

?
The velocity of detonation is a direct measure of the propagation of the rate of decomposition/detonation of the explosive.  Fiber optic cables are inserted into a length of charge (suitably away from the detonator if the charge is being overdriven(if the V(det) of the primary is greater than V(det) of the secondary) by the primary) and the fiber optics are hooked up to light detection electronics that can record time precisely.  The distance between the cables and the time it takes between each cable to register light is used as a direct means of measuring the detonation velocity of the explosive.  It is not an indirect measure of detonation by measuring the shockwave, you are directly measuring the reaction(detonation) rate in the explosive.

I'm pretty sure that is what renge ishyo was saying, just in an un-complicated way. I think he was saying that the shockwave does directly correlate with the denotation time.

You have an explosion whenever you have a high concentration of energy that is released to surrounding molecules in a short period of time.

What causes a high concentration of energy to be released in a short amount of time? Is it solely based on the nitrogen oxide to carbon ratio in a reaction?
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