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Question
If ΔG=−177Kcal for 2Fe(s)+32O2(g)→Fe2O3(s) and ΔG=−19Kcal for 4Fe2O3(s)+Fe(s)→3Fe3O4(s). What is the Gibbs free energy of formation of Fe3O4(s)?
If ΔG=−177Kcal for 2Fe(s)+32O2(g)→Fe2O3(s) and ΔG=−19Kcal for 4Fe2O3(s)+Fe(s)→3Fe3O4(s). What is the Gibbs free energy of formation of Fe3O4(s)?
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Solution
The correct option is B −242.3 kcal/mol
Given, 2Fe+32O2→Fe2O3....(i) △G=−177 KCal4Fe2O3+Fe→3Fe3O4....(ii) △G=−19 KCalDivide by (iii) in reaction (ii)43Fe2O3+13Fe→Fe3O4....(iii) △G=−193 KCalSimilarly, multiply by 43 in reaction (i)83Fe+43×32O2→43Fe2O3....(iv) △G=−177×43 KcalNow from (iii) and (iv)83Fe+2O2→43Fe2O3....(iv) −177×43 Kcal43Fe2O3+13Fe2→Fe3O4....(iii) −193 Kcal_____________________________________________Now adding (iv) and (iii) 3Fe(s)+2O2(g)→Fe3O4 △G=(−177×43−193) Kcal△G=−242.3 Kcal/mol
Given, 2Fe+32O2→Fe2O3....(i) △G=−177 KCal
4Fe2O3+Fe→3Fe3O4....(ii) △G=−19 KCal
Divide by (iii) in reaction (ii)
43Fe2O3+13Fe→Fe3O4....(iii) △G=−193 KCal
Similarly, multiply by 43 in reaction (i)
83Fe+43×32O2→43Fe2O3....(iv) △G=−177×43 Kcal
Now from (iii) and (iv)
83Fe+2O2→43Fe2O3....(iv) −177×43 Kcal
43Fe2O3+13Fe2→Fe3O4....(iii) −193 Kcal
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Now adding (iv) and (iii)
3Fe(s)+2O2(g)→Fe3O4 △G=(−177×43−193) Kcal
△G=−242.3 Kcal/mol
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