1. The problem statement, all variables and given/known data Using the information provided for energy changes associated with the formation of carbon dioxide, calculate the enthalpy for the formation of carbon monoxide. C(gr) + O2(g) → CO2(g) ΔH (-393.5 kJ mol-1) CO(g) + ½ O2 (g) → CO2 (g) ΔH (-283 kJ mol -1) C(gr) + ½ O2 (g) → CO(g) ΔH = ? 2. Relevant equations None really. 3. The attempt at a solution Reverse equation #2 to get CO2 (g) → CO(g) + ½ O2 (g) (+283 kJ mol -1). I think that's one of the steps anyway. Haven't done of these in ages. Do I sub in for CO2 in equation #1 and then add the enthalpy of formations? What's the next step?