Manganese dioxide MnO sub 2 times s , ΔH_f=−520.0kJ reacts with aluminum to form aluminum oxide Al sub 2 cap o sub 3 s , ΔH_f=−1699.8kJ and manganese according to the equation. 3 MnO sub 2 s plus 4 Al s rightarrow 2 Al sub 2 cap o sub 3 g plus 3 Mn s What is the enthalpy of the reaction? Use ΔH_rxn=∑(ΔH_f_1products)−∑(ΔH_f_1reactants)
Answer
A
negative 1 comma 839 point 6 kJ
B
negative 1 comma 179 point 8 kJ
C
1,839.6 kJ
D
1 comma 179 point 8 kJ
Explanation
Use the coefficients in the balanced equation when summing the formation enthalpies. The products total 2(−1699.8 kJ) + 3(0 kJ) = −3399.6 kJ; the reactants total 3(−520.0 kJ) + 4(0 kJ) = −1560.0 kJ. Therefore, ΔH_rxn = −3399.6 − (−1560.0) = −1839.6 kJ, which is choice A, negative 1,839.6 kJ.
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