Two of the oxides of iron are FcO and Fe304. Solid Fe exists in equilibrium with

Question

Two of the oxides of iron are FcO and Fe304. Solid Fe exists in equilibrium with one oxide at low temperatures and the other at high temperatures. The molar free energies of formation of these oxides are: Fe(s) + 1/2O2(g) = FeO(s) delta G degree = - 259,600 + 62.55T Joules 3Fe(s) + 2O2(g) = Fe3O4(s) delta G degree = - 1,091,000 + 312.8T Joules Determine which of the two oxides is in equilibrium with iron at room temperature and the maximum temperature at which this oxide is in equilibrium with iron

Explanation / Answer

For Fe+Fe3O4 =4FeO , ?G0 = 52,600?62.6 Tjoules.

?G0 = 0 at T = 840K, at which temperature Fe,FeO, and Fe3O4 exist in equilibrium.

At T < 840, ?G0 is negative and hence FeO is the stable oxide in equilibrium with Fe.

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