Let's find the enthalpy change for turning Carbon into Carbon Monoxide (C + 0.5 O2 -> CO). We can't measure this easily, but we know: Step 1: C + O2 -> CO2 (Energy = -393.5 kJ) Step 2: CO + 0.5 O2 -> CO2 (Energy = -283.0 kJ) Process: 1. Keep Step 1 as it is: C + O2 -> CO2 (ΔH = -393.5 kJ). 2. Reverse Step 2 to put CO on the right side: CO2 -> CO + 0.5 O2 (ΔH = +283.0 kJ). (Remember: reversing flips the sign!) 3. Add the two equations together: (C + O2) + (CO2) -> (CO2) + (CO + 0.5 O2) 4. Cancel out the common parts (CO2 on both sides and 0.5 O2 from O2): C + 0.5 O2 -> CO 5. Add the energy values: -393.5 + 283.0 = -110.5 kJ. The total heat change is -110.5 kJ.