Question

Determine the value of the enthalpy change, AH rxn, for the following reaction using the information below.
AP Chemistry
4 Al(s) + 3 MnO(s) → 2 AlO3 (s) + 3 Mn (s)
2 Al (s) + 3/2 O2(g) → Al2O3 (s)
AH = -1676 kJ
Mn(s) + O2(s) —> MnO2(s)
AН = -520.0 kJ

Answer 1

To determine the enthalpy change for the reaction 4 Al(s) + 3 MnO(s) → 2 Al2O3(s) + 3 Mn(s), we need to use the given enthalpy values for the individual reactions and apply Hess's law.

1. Reverse the second reaction:
Al2O3(s) → 2 Al(s) + 3/2 O2(g)
AH = 1676 kJ (given)
This gives us:
- AH1 = -1676 kJ

2. Double the third reaction and reverse it:
2 MnO2(s) → 2 Mn(s) + O2(g)
AН = -520.0 kJ (given)
This gives us:
- AH2 = 520 kJ

3. Combine the equations to get the desired reaction:
4 Al(s) + 3 MnO(s) → 2 Al2O3(s) + 3 Mn(s)
Add AH1 and -AH2 to get the enthalpy change for the desired reaction:
AH rxn = (-1676 kJ) + (520 kJ) = -1156 kJ

Therefore, the enthalpy change for the reaction 4 Al(s) + 3 MnO(s) → 2 Al2O3(s) + 3 Mn(s) is -1156 kJ.