The corrosion of iron can proceed through several intermediate solid oxides

CHEMISTRY · Multi-part · A Level · Chemistry · Thermodynamics · Thermodynamics

Problem

The corrosion of iron can proceed through several intermediate solid oxides. Three reactions measured at

298\,\text{K}

are listed below: Overall Reaction:

3\,Fe(s) + 2\,O_2(g) \to Fe_3O_4(s)

\Delta S^\circ_{\text{overall}} = -545.8\,\text{J mol}^{-1}\,\text{K}^{-1}

Step 1:

Fe(s) + 0.5\,O_2(g) \to FeO(s)

\Delta S^\circ_{1} = -143.5\,\text{J mol}^{-1}\,\text{K}^{-1}

Step 2:

3\,FeO(s) + 0.5\,O_2(g) \to Fe_3O_4(s)

\Delta S^\circ_{2} = \; ?

Step 2 involves the further oxidation of w\"ustite (

FeO

) to magnetite (

Fe_3O_4

). Use the information above to answer the following. (a) Calculate the standard entropy change

\Delta S^\circ_{2}

for Step 2. (b) State whether the sign of

\Delta S^\circ_{2}

is expected, considering the change in the amount of gaseous reactant, and justify your answer. (c) Compute the average entropy change per mole of

O_2

consumed in Step 2, and comment on how this compares to the value for Step 1.