Problem: Under certain nonstandard conditions, oxidation by O2(g) of 1 mol of SO2(g) to SO3(g) absorbs 89.6 kJ. The heat of formation of SO3(g) is –204.1 kJ/mol under these conditions. Find the heat of formation of SO2(g).

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FREE Expert Solution

We are asked to find the enthalpy of formation of SO2 under these conditions.

The oxidization of sulfur to SO3 is the formation reaction for SO3. Therefore, the enthalpy of reaction is the enthalpy of formation for SO3.


Balanced reaction: 

2 SO2(g) + O2(g) → 2 SO3(g)


ΔH°rxn=ΔH°f, prod-ΔH°f, react


Note that we need to multiply each ΔH˚f by the stoichiometric coefficient since ΔH˚f is in kJ/mol. 

Also, note that ΔH˚f for elements in their standard state is 0.



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Problem Details

Under certain nonstandard conditions, oxidation by O2(g) of 1 mol of SO2(g) to SO3(g) absorbs 89.6 kJ. The heat of formation of SO3(g) is –204.1 kJ/mol under these conditions. Find the heat of formation of SO2(g).