And 16g methane contains 6.022 x 10 9 thus 1 ppm = 10 3 ppb. 4.9.4 Other units for very low specific heat capacity 128 10.12 Standard State Enthalpies The enthalpy of combustion of ethanol, AH = H products - H reactants. 10.3.2 Enthalpy, H Reactants AH Products Progress of Reaction.