[the_zom]

I've run into something that I don't understand and I was hoping for a little guidance.

Here's the question:

Iron (II) sulfide ore is roasted according to the following chemical equation:
4 FeS + 7 O₂ --> 2 Fe₂O₃ + 4 SO₂      :delta:H_c = -2446 kJ

a) Rewrite this equation including the energy as a term in the equation

b) What is the molar enthalpy of Iron (II) sulfide in this reaction?

c) What is the molar enthalpy of Iron (III) oxide in this reaction?

My answers:

a) 4 FeS + 7 O₂ --> 2 Fe₂O₃ + 4 SO₂ + 2446 kJ

b) The molar enthalpy of FeS is 611.5 kJ/mol (my reasoning being that 4 mol of FeS undergoes combustion, so the molar enthalpy must be 2446kJ/4)

c) I have absolutely no idea how to approach this one.

I fear my reasoning may not be sound for b) but if it is, I don't know how to apply it to c).

Any help would be much appreciated.

[RickyC]

a) Rewrite this equation including the energy as a term in the equation

First of all the initial reaction you're given is: 4 FeS + 7 O2 --> 2 Fe2O3 + 4 SO2      ΔH = -2446 kJ

Now the question asks you to include the energy as a term in the eqn. As you know energy = heat. And since the rxn is exothermic (ΔH is negative) then heat is given off in the rxn.

So the answer to  part a is : 4 FeS + 7 O2 --> 2 Fe2O3 + 4 SO2 + heat.
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b) What is the molar enthalpy of Iron (II) sulfide in this reaction?

You are correct in your reasoning for part b, but the enthalpy for the FeS is minus 611.5 kJ
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c) What is the molar enthalpy of Iron (III) oxide in this reaction?

This is the exact same as the last part - divide 2446 by 2 = 1223 kJ (the reason this one is positve is because you are going by the reverse rxn - and if you reverse a rxn then you must also change the sign of the ΔH)

[rabolisk]

Molar enthalpy of what? It does not make any sense to say molar enthalpy of x. Do you mean the molar enthalpy of formation of x?

[the_zom]

Molar enthalpy of what? It does not make any sense to say molar enthalpy of x. Do you mean the molar enthalpy of formation of x?

Welcome to my nightmare.  The way I worded the question was a direct transcription of the question on my assignment.

I am less than impressed by the calibre of this correspondence course I'm taking.

[Zeppos10]

if you look up the enthalpy of formation of the compounds involved you will find the following (approximate) values in kJ/mol: FeS(s)= -102, O2=0, Fe2O3= -824, SO2=-298.
These values cannot be obtained from the given combustion reaction alone.