Carbon reacts with oxygen to produce carbon dioxide (CO2 (g), Delta. Hf = –393. 5 kJ/mol) according to the equation below. Upper C (s) plus 2 upper O subscript 2 (g) right arrow upper C upper O subscript 2 (g). What is the enthalpy change of the reaction? Use Delta H r x n equals the sum of delta H f of all the products minus the sum of delta H f of all the reactants. –393. 5 kJ –196. 8 kJ 196. 8 kJ 393. 5 kJ.