Calculate Heat of Formation for SO3 Gas using Hess' Law - Step by Step Guide"

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To calculate the heat of formation for one mole of SO3 gas using Hess' Law, the reaction equations provided must be manipulated appropriately. The first reaction shows the formation of SO2 from S8 and O2, releasing 2378.4 kJ, while the second reaction shows SO2 reacting with O2 to form SO3, releasing 99.0 kJ. By multiplying the second equation by 8, the overall balanced equation becomes S8 + 12O2 → 8SO3. The total heat change is calculated by combining the heats from both reactions, resulting in -3170.4 kJ for 8 moles of SO3, which gives a heat of formation of -396.3 kJ for one mole of SO3. This method effectively uses Hess' Law to determine the desired heat of formation.
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Compute the heat for formation of one mole of SO3 gas from the following data:

Sorry I don't know how to do subscripts...

S8(s) + 8O2(g) --> 8SO2(g) + 2378.4 kJ
SO2(g) + 1/2O2(g) --> SO3(g) + 99.0 kJ

I don't have a clue where to start...
 
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Since you are finding out the heat for formation of one mole of SO3 gas, it is necessary for you to find out the reaction equation for the foramation of SO3 gas using the given data first. By addition/subtraction/multiplication/division the given data, you can find out the equation, and therefore find out the heat for formation.
 
So is this right?

I'm going to multiply the second equation by 8...

S8(s) + 8O2(g) --> 8SO2(g) + 2378.4 kJ
8SO2(g) + 4O2(g) --> 8SO3(g) + 792 kJ

Balanced equation (well adding the both of them together):

S8(s) + 12O2(g) --> 8SO3(g)

________________________________________________________________
-2378.4 kJ + (-792 kJ) = -3170.4 kJ

-3170.4 kJ/8 mol x 1 mol = -396. 3 kJ[/color] (the mol's will cancel)
 
Um, Yes. I think it is right!
 

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