First of all i'm no chemist, this is not homework and if you need further clarification please ask. I'll be happy to provide!

Imagine that you:

  • have 1 kg of any given chemical X
  • A car battery
  • A semi-controlled combustion chamber (chamber temp is initially 20ºC, pressure is 1atm, the chamber is either vacuum or filled with atmosphere "air"...)
  • As much atmosphere "air" as you want, initially at 20ºC...
  • A not so potent air-pressurizer... you might be able to get 3atm out of it...

The goal here is to get the most energy out of reaction as possible. So the question is: What chemical is X?

Further details:

  • X doesn't have to be consumed all at once as in a explosion reaction... Damage/Destruction is not the goal
  • If you can combine X with something in the air, and then use it to fuel the reaction, increasing the energy output, great!
  • 1
    $\begingroup$ AFAIK in practice good old gasoline has most energy-per-gram as long as you include storage tank into weight. Granted, theoretically hydrogen should be the most effective in the case, but it is too hard to store at average temperature. $\endgroup$
    – permeakra
    Oct 15, 2014 at 18:19

1 Answer 1


this is a way too generalized question. you certainly need experimental data or extensive screening to make sure you are on the top of the volcano plot. have you heard the term adiabatic flame temperature? The ratio of inert to gasoline/fuel is a determining factor to get high combustion energy. For example the adiabatic flame temperature for methane is higher for a mixture of methane and air with 5-15 mol% methane. 5-15 mol% methane can ignite without any external source of fire.

Please see the attached link to compare fuels according to their energy density: http://en.wikipedia.org/wiki/Energy_density

And for your question you can't have two variables to optimized with one equation, either you have to specify the chemical X or you have to specify what is the output energy of this process. If you know the chemical X with it's thermodynamic property than using basic heat balance equation you can calculate the output energy.

  • $\begingroup$ isn't there a way (possibly a equation) that given a molecular structure and a reagent it outputs the "delta" energy of the reaction? If so, as a developer i could "brute-force" it... of course i would use a few heuristics and possibly some machine-learning along with backtracking... $\endgroup$
    – Leonardo
    Oct 16, 2014 at 14:42
  • $\begingroup$ That's a good point. Electronic structure theory can be applied for preliminary screening. Actually i am working on computational catalysis and one of my main objective is to find better catalysts for reaction. Here i optimize each reactants, intermediates and products with appropriate level of theory and then locate the transition state. This will give you both the reaction energy and activation energy. Moreover if you put them in a suitable microkinetic model you will get the reaction rate with rate limiting step. You can use DFT for faster calculation or you can use Hartree-Fock approach. $\endgroup$ Oct 16, 2014 at 16:05
  • $\begingroup$ hmmmmmmmm thats very interesting!!! i smell nobel prizes... $\endgroup$
    – Leonardo
    Oct 16, 2014 at 17:58

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