Given the equations below, what is the heat of reaction for the process in which carbon monoxide is formed from its elements?

c(s, graphite) + o2(g) → co2(g), ∆h = –393.5 kj

co2(g) → co(g) + ½o2(g), ∆h = 283.0 kj

The formation equation for carbon monoxide is:
C(s) + 1/2O2(g) --> CO(g).
We know that all of the elements and compounds are on the correct sides of the equations (C and O on left and CO on the right). The coefficients are also correct, so all we have to do is cancel out. The CO2's cancels out, and the O2's cancel out and leave a 1/2O2 on the top reaction. Finally, all we have to do is add up the heats of reactions for our final answer. As -393.5 + 283.0 = -110.5, our final answer is -110.5 kJ.

Hope this helps!