Nitrogen dioxide, NO2(g) (Delta. Hf = 33. 84 kJ/mol), is decomposed according to the following reaction: 2 upper N upper O subscript 2 (g) right arrow upper N subscript 2 (g) plus 2 upper O subscript 2 (g). What is the enthalpy change when 2. 50 mol of nitrogen dioxide decomposes? 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. 13. 5 kJ of energy released 13. 5 kJ of energy absorbed 84. 6 kJ of energy released 84. 6 kJ of energy absorbed.