Hi everyone, first time poster here. I've lurked on the site in the past, and really appreciate the wealth of resources that are provided here, especially the math section! Anyway, I have a question that I'm sure is very elementary but for some reason I have failed to grasp and therefore has produced bogus results. I'm trying to calculate the ΔH of a gas reaction that is as follows: 2CH2=CHCH3 + 2NH3 + 3O2 → 2CH2=CHCN + 6H2O So what I did was sum up [moles of bonds * bond enthalpy for bonds broken] and subtract [moles of bonds * bond enthalpy for bonds formed] from that. My values looked like this: [(2 mols C=C * 598) + (4 mols C-H * 416) + (2 mols C-H * 416) + (2 mols C-C * 356) + (6 mols C-H * 416) + (6 mols N-H * 391) + (3 mols O=O * 498)] - [(4 mols C-H) + (2 mols C=C * 598) + (2 mols C-H * 416) + (2 mols C-C * 356) + (2 mols C-N * 285) + (12 mols H-O * 467)] = 162 kJ Just looking at how messy that came out, I knew before I began calculating that my method of approach must have been flawed. So, can anyone point out how to calculate deltaH? My text gives only the most elementary of examples, like CH4 + 2O2 ---> CO2 + 2H2O, so that hasn't helped me with a more advanced problem like this one. Thanks in advance to anyone who could give me some advice.