Manganese dioxide (MnO2(s), Delta. Hf = –520.0 kJ) reacts with aluminum to form aluminum oxide (AI2O3(s), Delta. Hf = –1699.8 kJ/mol) and manganese according to the equation below. 3 upper M n upper O subscript 2 (s) plus 4 upper A l (s) right arrow 2 upper A l subscript 2 upper O subscript 3 (g) plus 3 upper M n (s). What is the enthalpy 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..