Ammonia, NH3 (Delta. Hf = â€"46. 2 kJ), reacts with oxygen to produce water (Delta. Hf = â€"241. 8 kJ) and nitric oxide, NO (Delta. Hf = 91. 3 kJ), in the following reaction: 4 upper N upper H subscript 3 (g) plus 5 upper O subscript 2 (g) right arrow 6 upper H subscript 2 upper O (g) plus 4 upper N upper O (g). What is the enthalpy change for this 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. â€"900. 8 kJ â€"104. 6 kJ 104. 6 kJ 900. 8 kJ.