What is the enthalpy of reaction for CH4 + 2O2 -> CO2 + 2H2O, if the conversion of CH4 is 50%, and heat of formation of CH4, O2, CO2, and H2O are 10 J, 0, 6 J and 4 J?

Correct Answer: 2 J
Heat of reaction = 2*4*0.5 + 6*0.5 + 10*0.5 – 2*0 – 10 = 4 + 3 + 5 – 10 = 2 J.