I thought when you are finding the change in enthalpy for a rxn you go: pdt-reactants? I am confused by the topscore solution in which you gotta find the change in enthalpy for: 2C(s)+O2(g)---> 2CO (g). I would try to rewrite the question, but it's too hard. For anyone who has topscore, i think you know this question. It is on test 2 for genchem, I think question 57 (gchem 17). I would really appreciate the help.