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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: NewtoAtoms on March 08, 2009, 12:53:49 PM

Title: determine the temperature at which carbon can reduce iron (III) oxide to iron
Post by: NewtoAtoms on March 08, 2009, 12:53:49 PM

2Fe₂O₃ (g)  +  3C (s) ----------> 4 Fe (s)  +  3 CO₂ (g)

I am assuming that this is an enthalpy question, therefore I would calculate it according to:

   ΔH^o_rxn= [4(0 kJ/mol) + 3(-393.5 kJ/mol)] – [2(-824.2 kJ/mol) + 3(0 kJ/mol)] =
   ΔH^o_rxn= [-1180.5 kJ/mol] – [-1648.4] = 467.9 kJ/mol

This means that 2 moles of Fe₂O₃ and 3 moles of C will need to 467.9 kJ/mol of heat added to be reduced to iron.
However I am confused because this is not answering the question : Determine the temperature at which carbon can reduce iron (III) oxide to iron.

Can anyone help direct me on the right path?
I would be so grateful for anyone's help.

Thank you so much

NewtoAtoms

Title: Re: determine the temperature at which carbon can reduce iron (III) oxide to iron
Post by: Astrokel on March 08, 2009, 01:05:59 PM

What were you given? Enthalpies only? What about heat capacities?

Title: Re: determine the temperature at which carbon can reduce iron (III) oxide to iron
Post by: NewtoAtoms on March 08, 2009, 01:14:02 PM

I wasn't give any more information than the question itself, therefore I was stuck. 
Heat capacities are in the same chapter as enthalpies and I don't know which one is the one to use here?

I know that enthalpies show whether a reaction is endothermic or exothermic and that heat capacities is the amount of heat required to raise the temperature of a given quantity of a substance by one degree C. 

I thought when asking to determine the temperature "at which carbon can reduce iron (III) oxide to iron, it referred soley to enthalpy. 

Can you explain why you might suggest heat capacities???

Thank you for your time.

Title: Re: determine the temperature at which carbon can reduce iron (III) oxide to iron
Post by: Astrokel on March 08, 2009, 02:16:29 PM

Quote

Can you explain why you might suggest heat capacities???

If you assume it is a closed system,  :delta: q = - :delta: w. You could relate it to temperature if you have values for molar heat capacities.

Title: Re: determine the temperature at which carbon can reduce iron (III) oxide to iron
Post by: shanmac on October 15, 2012, 05:53:30 PM

I also am working on this question and am wondering if I have done it properly... could someone let me know if I am on the right track?  Here is my leg work:

ΔH of CO2 (g) = -393.5 kJ/mol ∴ 3 mol CO2 (g) = -1180.5 kJ/mol
ΔH  of Fe (s) = 0 kJ/mol ∴ 4 mol Fe (s) = 0 kJ/mol
ΔH  of Fe2O3 (s) = -822.2 kJ/mol ∴  2 mol Fe2O3 (s) = -1644.4 kJ/mol
ΔH  of C (s) = 0 kJ/mol ∴ 3 mol C (s) = 0 kJ/mol
ΔH°rxn= ∑nΔH_f(products) - ∑nΔHf(reactants)

ΔH°rxn= (-1180.5) + 0 - (-1644.4) + 0 = 463.9 kJ/mol

S° of CO2 (g) = 213.6 J/K•mol ∴ 3 mol CO2 (g) = 640.8 J/K•mol
S°  of Fe (s) = 27.2 J/K•mol ∴ 4 mol Fe (s) = 108.8 J/K•mol
S°  of Fe2O3 (s) = 90.0 J/K•mol ∴  2 mol Fe2O3 (s) = 180.0 J/K•mol
S°  of C (s) = 5.69 J/K•mol ∴ 3 mol C (s) = 17.07 J/K•mol
S°rxn= ∑S°(products) - ∑S°(reactants)

S°rxn= 552.53 J/K•mol = 0.5525 kJ/mol

T = ΔH
      ΔS

T = 463.9 kJ/mol ÷ 0.5525 kJ/mol = 839.6 K

Am I on the right track?  Thanks in advance...