Calculate the enthalpy of formation of maganese (IV) oxide based on the following information.

Question

4Al(s) + 3MnO2(s) --> 3Mn(s) + 2Al2O3(s) Delta H = -1790 kJ

2Al(s) + 3/2O2 (g) ---> Al2O3 (s) Delta Hf = -1676 kJ

Answer 1

we need twice the second reaction to make 2Al2O3, then the first reaction reversed to make three moles of MnO2

Hr=2*(-1676kJ)+1790kJ
but we make 3 moles MnO2
hf=Hr above/3 kJ/mole