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Enthalpy of Combustion for long compounds

Hi Everyone!I need help in calculating the enthalpy of (complete) combustion theoretically of long compounds such as C20H23N7O7. I have found that when combusting compounds with nitrogen in, the product is N2.

From what I have read online:
the enthalpy of combustion = formation enthalpy of products - formation enthalpy of
reactants

However the problem is that I don't know the enthalpy of formation of C20H23N7O7. Ive looked online everywhere and I couldn't find it. Is there a way to calculate the enthalpy of formation of this compound.
I also tried Hess's law but i still need the enthalpy of formation of the long compound. I also don't know the enthalpy of reaction

Please help me out. Is there any way forward?
Any help will be greatly appreciated.

Reply 1

username913907

Original post by jjaved

To which of the many isomers of C20H23N7O7 are you referring? http://www.chemspider.com/Search.aspx?q=C20H23N7O7

Reply 2

username913907

Original post by jjaved

In more helpful news... try searching by it's common name. Perhaps folinic acid?

Reply 3

jjaved

Original post by JMaydom

In more helpful news... try searching by it's common name. Perhaps folinic acid?

Im trying to find the enthalpy of 10-Formyltetrahydrofolate instead of folinic acid (both of which have the same molecular formula)

Reply 4

username913907

Original post by jjaved

Im trying to find the enthalpy of 10-Formyltetrahydrofolate instead of folinic acid (both of which have the same molecular formula)

OK, but they will have different enthalpies of formation so it's important. Even allotropes (e.g. diamond and graphite) have different formation enthalpies.
Find it for your molecule and you're sorted.

Reply 5

jjaved

Original post by JMaydom

I agree with you, however that is the problem I am facing. I have tried hard to find out the enthalpy of formation of 10-Formyltetrahydrofolate (C20H23N7O7) but I'm having no luck. Hence, I don't know how I can calculate the enthalpy of combustion of 10-Formyltetrahydrofolate without its enthalpy of formation.

Is there any way forward?

Reply 6

username913907

Original post by jjaved

Short of the awfully crude method of average bond enthalpies I can't think of one. Maybe just use a similar compound.

Reply 7

jjaved

Pardon me if this sounds silly, but is there a way to calculate the enthalpy of formation of a compound (preferably C20H23N7O7,10-Formyltetrahydrofolate) without knowing its enthalpy of combustion or reaction?

(edited 8 years ago)

Reply 8

charco

Study Forum Helper

Original post by jjaved

Apart from the bond enthalpy method suggested by JMaydom, no.

Reply 9

jjaved

Original post by JMaydom

Short of the awfully crude method of average bond enthalpies I can't think of one. Maybe just use a similar compound.

Please could you perhaps briefly explain this method? :smile:

What I understand of that method is to add up all the average bond enthalpies of the bonds in the compound and use that as the enthalpy of formation.

Pardon me if that was completely wrong.

Reply 10

Pigster

Add up all of the bond enthalpies of all of the bonds of the elements needed to make your compounds, then subtract all the bond enthalpies of the bonds in your compound.

The answer should be a bit close to the true value.