Question

C2H5O2N is an important compound. The combustion reaction of glycine proceeds according to this equation:
4C2H5O2N + 9O2 ---> 8Co2 +10H2O +2N2
which is = -3857 kJ

Given CO2 is -393.5 kJ/mol
Given H2O is -285.6

Calculate the standard molar enthalpy of formmation of glycine.

Answer 1

What I have looks like this:

4X +9(0) - 8(-393.5) +10(-285.8) +2(0)
Products - Reactants
with 0 being the natural elements

4X - -6003 does not get me the answer so what am I doing wrong?

Answer 2

I think it's too easy to get a sign wrong trying to do all of it at one time.
DHrxn = [n*DHproducts]-[n*DHreactants]
-3357 = (8*DHfCO2)+(10*DHH2O)] - (4*DHgly)
-3357 = (8*-393.5) + (10*-285.8)] - 4X
-3357 = (-3148)+(-2858)] - 4X
-3357 = -6006 - 4X; now I switch and
4X = -6006 + 3357 and solve for X.
Something like 662 kJ/mol but that isn't exact. I ALWAYS check these things by
DHrxn = (n*DHproducts)-(n*DH reactants) and see if I come out with 3357 kJ for the reaction.