If DeltaG = - 177 K cal for (1) 2 Fe(s) + (3)/(2)O_(2)(g) rarr Fe_(2)O_(3)(s) and DeltaG = - 19 K cal for (2) 4 Fe_(2)O_(3)(s) + Fe(s) rarr 3 Fe_(3)O_(4) (s) What is the Gibbs free energy of formation of Fe_(3)O_(4) ?

If DeltaG = - 177 K cal for (1) 2 Fe(s) + (3)/(2)O_(2)(g) rarr Fe_(2)O

1.	If DeltaG = - 177 K cal for (1) 2 Fe(s) + (3)/(2)O_(2)(g) rarr Fe_(2)O_(3)(s) and DeltaG = - 19 K cal for (2) 4 Fe_(2)O_(3)(s) + Fe(s) rarr 3 Fe_(3)O_(4) (s) What is the Gibbs free energy of formation of Fe_(3)O_(4) ?
Answer» `+ 229.6 ("kcal")/("mol")` `-242.3 ("kcal")/("mol")` `-727 ("kcal")/("mol")` `-229.6 ("kcal")/("mol")` Solution :Reaction for formation of `Fe_(3)O_(4)` is `3Fe_((s)) + 2O_(2(g)) RARR Fe_(3)O_(4(s))` …(1) And we have reactions as follows: `2Fe_((s)) + (3)/(2) O_(2(g)) rarr Fe_(2)O_(3(s))` …(2) `4Fe_(2)O_(3(s)) + Fe_((s)) rarr 3Fe_(3)O_(4)` ..(3) Eq (1) `= (Eq(2) XX 4 + Eq (3) xx 1)/(3)` So, `Delta G = (4 (-177) + (-19))/(3)` `= -242.3` Kcal/mole