Hello,
is there a calculator that computes the energy released in a chemical reaction given the reagents and the products.
That is: If I have a molecule A, B and C, with A being the reagent and B+C the products, what would be the energy released in splitting A into B and C? For instance, the degradation of tetramethylbenzidine by peroxidase; how much energy is released?
Thank you
Unless you have the formation enthalpies of the parts, that is not straightforward, but before we start with that, let's set something clear:
Peroxidase is an enzyme and therefore a catalyst which means that it makes the reaction faster but it does not change the reaction enthalpy. Therefore when you look for data you do not need a context with peroxidase, all you need are the formation enthalpies of tetramethylbenzidine and the decomposition products.
A good tool to search for such data is CAS scifinder because you can actually search for whole reactions.
Now, if there is no data, you have two options:
a) measure the formation enthalpy of tetramethylbenzidine and your products or just measure the reaction enthalpy directly in a calorimeter. Since at least TMB is not that expensive, that shouldn't be that complicated.
b) perform quantum chemical calculations in connection with statistical thermodynamics. That is harder to do and requires experience with the corresponding software plus it is of course less accurate than experimental data.
add up the bond energies in the starting materials and the products. The difference gives you an estimate of the energy difference
Stefan T. Orszulik Since Tetramethylbenzidine has two aromatic systems affecting each other and additionally substituents with -I and +M effects, I don't think the incremental bond adddition method is going to work very well on these.
do you know the heat of formation or the heat of combustion for each material? If so, you could work it out that way.
I don't have experimental data, neither there are data on PubMed that I know of. I only have the structural formulae of the reagent and product. I have found this link to calculate the enthalpy http://www.kentchemistry.com/links/Kinetics/BondEnergy.htm
Is there a quicker ready-made calculator? Something I provide the structure, it tells me the enthalpy.
Thanks
This is the incremental method which Stefan Orszulik described in his first post which gives you a good approach if you have only "normal" bonds. However, your molecule has interacting aromatic rings with influential substituents and that will probably turn this approach rather problematic.
I don't know what the products are but if the benzidine rings remain intact then it might not be so difficult to work out. Just do the bond energies if the bonds that are changed. That should do it.
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