My Name Yuly from chemistry department ITS, Indonseia. I was tried to calculate the combustion enthalpy of methanol. The obtained results of enthalpy of methanol, oxygen, carbon dioxide, and water are 34.716; 5.008; 7.965 and 14.82 Kcal/mol respectively. After I calculated, the result of combustion enthalpy of methanol -4.623 KCal/mol or -19. 416 Kj/mol. This result far from the literature which mention about -700 kJ/mol.

We tried to calculate using the others software Gaussian and Orca. We founded the result from this calculation almost the same with the literature. And we find that the value of enthalpy in Qchem about the same with total energy thermal that is stated in Gaussian.

Could some one have the same experience with me. Did I take the wrong value from output of Qchem?

For combustion enthalpy from Gaussian we used
Sum of electronic and thermal Enthalpies= -115.658696
(still in hertree, then we convert to kJ/mol) We obtained abou -600 kJ/mol this result near the literature.

Thank you.

It would be helpful if you could post an input file and the relevant portion of your output file, indicating which values you have taken to get the numbers mentioned above.

Thankyou for your reply.
All the calculation I put in this folder.

Yuly, Q-Chem prints enthalpy as just the thermal corrections rather than printing the full electronic + thermal enthalpy. To calculate total enthalpy in Q-Chem (equivalent to how other software you mentioned do it), you need to add the enthalpy correction to the total SCF electronic energy (after converting kcal/mol to Hartree).