Solution: Calculate the ΔH (in kJ) for the reaction:3 Fe2O3 (s) + CO (g) → CO2 (g) + 2 Fe3O4 (s)             ∆Hrxn = ?Given the following reactions:Fe2O3 (s) + 3 CO (g) → 2 Fe (s) + 3 CO2 (g)                 ∆H1 = −28. 0 kJ3 Fe (s) + 4 CO2 (g) → 4 CO (g) + Fe3O4 (s)                 ∆H2 = +12. 5 kJA. -59.0B. +40.5C. -15.5D. -109E. +109

Problem

Calculate the ΔH (in kJ) for the reaction:

3 Fe2O3 (s) + CO (g) → CO2 (g) + 2 Fe3O4 (s)             ∆Hrxn = ?

Given the following reactions:

Fe2O3 (s) + 3 CO (g) → 2 Fe (s) + 3 CO2 (g)                 ∆H1 = −28. 0 kJ

3 Fe (s) + 4 CO2 (g) → 4 CO (g) + Fe3O4 (s)                 ∆H2 = +12. 5 kJ

A. -59.0
B. +40.5
C. -15.5
D. -109
E. +109

Solution

We’re being asked to determine the enthalpy change (ΔHrxn) for the chemical reaction:


3 Fe2O3 (s) + CO (g) → CO2 (g) + 2 Fe3O4 (s)   


We can use Hess’s Law to determine the enthalpy change of the overall reaction from the given reactions:

Fe2O3 (s) + 3 CO (g) → 2 Fe (s) + 3 CO2 (g)                 ∆H1 = −28. 0 kJ

3 Fe (s) + 4 CO2 (g) → 4 CO (g) + Fe3O4 (s)                 ∆H2 = +12. 5 kJ


We now need to find a combination of the two reactions that when added up, gives us the overall reaction.


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