34At first it may seem non-sensical for the carbon dioxide product of this reaction to have a negative energy, until you realize the zero values given to both the carbon and oxygen reactants are entirely arbitrary. Viewed in this light, the negative heat of formation for CO2 is nothing more than a relative expression of chemical potential energy in reference to the elements from which CO2 originated. Therefore, a negative ΔHf value for any molecule simply tells us that molecule has less energy (i.e. is more stable) than its constituent elements.