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SaintJude

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Metals are extracted from their ores by a wide variety of techniques. An example of an extraction is of iron from its oxide, described by the following equation:

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

The relative ease of extraction of a metal from its oxide can be estimated using the Ellingham diagram, which is shown below. This diagram plots the the free energies of formation of various oxides per mole of consumed oxygen as a function of absolute temperature.

i3iMx.png


1.) Elemental carbon is most likely to reduce Fe2O3 in which of the following temperature ranges?

A. 500-1000 K
B. 500-1500K
C. Below 1000K
D. Above 1000K

2. When ferric oxide is produce to obtain iron metal, CO2 or CO can be produced. The production of carbon dioxide

A.) is directly proportional to the temp
B. is inversely proportional to the temp
C. is independent of the temp
D.) requires cooling of the CO.

Answer for both: D
 

7175pank

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lol k.

1. G CO = G Fe2O3 at ~1000k. Since G Fe2O3 > G CO when T > 1000 -> G of reactants > G products -> G = G(p) - G(r) < 0

2. It's actually B lol Gibbs free energy for CO decreases with temperature increases, making it the more favorable product over CO2 which causes the creation of CO2 to decrease with temperature.
 
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SaintJude

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Jan 4, 2012
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lol k.

1. G CO = G Fe2O3 at ~1000k. Since G Fe2O3 > G CO when T > 1000 -> G of reactants > G products -> G = G(p) - G(r) < 0

2. It's actually B lol Gibbs free energy for CO decreases with temperature increases, making it the more favorable product over CO2 which causes the creation of CO2 to decrease with temperature.

Ok, both answers are actually D.

But for No.1... So are you essentially trying to identify a section where the free energy of Fe2O3 > CO's free energy b/c you're looking for dG < 0.

Edit: Actually now No. 29 makes sense.

I see why answer for No.29 is D. The production of CO2 depends on basically awaiting when the production for CO is unfavorable.

At a low temperature, the reaction involving CO is positive dG>0
But at a low temperature, the reaction involving CO2 is less positive and thus more favorable.
 
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