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Heat of Formation


Caesius
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A while back my chemistry professer wanted to teach me about explosives and how to develop newer and better explosives. I accepted and we started to learn about RDX and different related explosives with the RDX base. Soon I started to develop my own explosives (all in theory of course). But, I stubbled upon a very interesting property. I wanted to find out which chemical caused RDX to have and extreamly high negative heat of formation. Through a bunch of calculations I descovered that nitrites caused RDX to have a positive Hf. Whereas peroxy acids and hydroxides decreased the Hf. The more of each group I added to the RDX molecule the greater its effects. I tried this again but on a benzine molecule and graphed the results on an excel spreadsheet, I noticed a pattern. Next, I tried to see if combining groups on the benzine molecule would be the averageHf of the two graph functions. The results were nearly perfect. Your thoughts?

 

 

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  • 2 weeks later...

That's an excellent beginning.

 

Perhaps the first cause for heat of formation are the individual bonds between the atoms. Oxygen bonded to carbon or hydrogen releases much heat, but to nitrogen little. And nitrogen bonds best with itself in N2.

 

The you have strain within the molecules, for instance in cyclopropane, diasterane, stellane... You may - or not - view multiple bonds as a special case of strained bonds.

 

Resonances lower the heat of formation, like in benzene or guanidine.

 

Steric hindrance increases the heat of formation, but not much, and highly hindered molecules tend not to exist or be difficult to synthesize.

 

Important to energetic compounds is that stability is loosely linked with heat of formation. Cubane for instance is quite stable.

 

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If you study energetic compounds, please convince yourself that rocket propellants have nothing to do with explosives.

 

Using hundreds of tons of propellants is dangerous enough that rockets want very safe propellants. Explosives, even little sensitive like nitromethane, are excluded, and people think twice and thrice before using hydrogen peroxide. Components that polymerize, like ethylene, are excluded as well. Rockets strongly prefer compounds with a flash well above a sunny day. And toxic compounds like hydrazine and its parents are being suppressed currently.

 

As a consequence, mono-propellants (like nitromethane) aren't used on rockets nor spacecraft, only on paper. And once you've several propellants, you get more reaction heat by putting C, H and sometimes N and Al in the fuel, and all O in the oxidizer.

 

Exotic propellants like NF3, F-Cl-O combinations and the like, are all abandoned. Beware most documents and books are historic, and much Internet frenzy (propyne...) is personal work that was never used.

 

As well, launchers to space have different requirements (performance through liquids) than missiles (readiness through solids). Missile propellants are more varied, launcher propellants have boiled down to 4 combinations presently. Which doesn't mean progress has ended: we need strained hydrocarbons, stable and cheap; non-toxic replacements for methylhydrazine, quickly pyrophoric with N2O4 and efficient and cheap; non-toxic replacements for N2O4 and efficient and cheap; solids better than Al+polybutadiene+NH4ClO4.

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