[MelgaShop]

Hi all! This is my 1st message in here and I'd like you to check if my exercise is right or not.
Here it is:


The combustion heat of 1 mol of H2, C, CH4 and C2H6 are: -68.32; -94.05; -212.80; -372,82 Kcal/mol

Now, here it is the deal:
What's the formation heat of CH4?

I've tried to do it and since I don't have its solution, I'd like you to check if it's correct or not:

C+O2 -> CO2
2*(H2+1/2 O2 -> H2O)
CO2 + 2H2O -> CH4 + 2O2
=====================
C+2H2 -> CH4


Hf (CH4)= 212.80 -  ( - 94.05 + (2*-68.32)) = 442.8 Kcal/mol (more or less)

Is this correct?
Thanks in advance!

[Donaldson Tan]

With reference to the diagram,

dH_f(CH₄) = dH_c(C) + 2 dH_c(H₂) - dH_c(CH₄)

[xiankai]

dont forget to add the O2 to the reagents too, although they do not contribute to the Born-Haber cycle, u must ensure all reagents/products are accounted for.