TPR genchem problem

[cornpops21]

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2 SO3(g) --> 2 SO2 (g) + O2 (g) delta H = 198 kJ

2 SO2 (g) + O2 (g) --> 2 SO3 (g) delta H = -198 kJ

The heat of formation of SO3 (g) is -396 kJ/mol. What is the heat of formation of SO2 (g)?

A. -396 kj/mol
B. -297 kj/mol
C. -198 kj/mol
D. -495 kj/mol

The answer is B. Can anyone explain it? This is a diag question and the explanation cuts off for some reason.

 

[Bu2009]

2 SO3(g) --> 2 SO2 (g) + O2 (g) delta H = 198 kJ

2 SO2 (g) + O2 (g) --> 2 SO3 (g) delta H = -198 kJ

The heat of formation of SO3 (g) is -396 kJ/mol. What is the heat of formation of SO2 (g)?

A. -396 kj/mol
B. -297 kj/mol
C. -198 kj/mol
D. -495 kj/mol

The answer is B. Can anyone explain it? This is a diag question and the explanation cuts off for some reason.

Heat of formations by def is teh amount of energy required to make one mole of a compound from its consitituent element in their natural or standard state.

O2 is diatomic natural state for oxygen so its heat of formation is zero in this case. So u can ignore it. There are other things like pure solids and liquids thats in this category.

So for formula for this is

Delta Heat Rxn = Sum of n x delta heat of products ) - (sum of n x delta heat of reactants).

n is the stoichiometric coefficient applied to w/e ur species are in ur equation.

So in your case u can really use either equation to solve for ur answer.

I picked the bottom one.

so

2 SO2 (g) + O2 (g) --> 2 SO3 (g) delta H = -198 kJ
given that SO3 heat of formation = -396

so you would do -198 KJ = 2(-396 KJ)- 2(So2) or {products - reactants)

so u can just set So2 to X and solve for ur answer. (1 mole only will be your heat of formation for SO2).