Question

The chemical reaction that causes iron to corrode in air is given by
4Fe + 3O2→2Fe2O3 in which at 298 K
ΔHrxn= 1684 kJ
ΔSrxn= 543.7 J/K

Part A. What is the standard Gibbs free energy for this reaction? Assume the commonly used standard reference temperature of 298 K.

Part B. What is the Gibbs free energy for this reaction at 3652 K? Assume that Delta H and Delta S do not change with temperature.

Answer 1

Answer :

(A) The value of $\Delta G^o$ at 298 K is, 1521.9 kJ

(B) The value of $\Delta G^o$ at 3652 K is, -301.59 kJ

Explanation :

Part A :

$\Delta G^o=\Delta H^o-T\Delta S^o$

where,

$\Delta G^o$ = standard Gibbs free energy  = ?

$\Delta H^o$ = standard enthalpy = 1684 kJ = 1684000 J

$\Delta S^o$ = standard entropy = 543.7 J/K

T = temperature of reaction = $298K$

Now put all the given values in the above formula, we get:

$\Delta G^o=(1684000J)-(298K\times 543.7J/K)$

$\Delta G^o=1521977.4J=1521.9kJ$

Part B :

$\Delta G^o=\Delta H^o-T\Delta S^o$

where,

$\Delta G^o$ = standard Gibbs free energy  = ?

$\Delta H^o$ = standard enthalpy = 1684 kJ = 1684000 J

$\Delta S^o$ = standard entropy = 543.7 J/K

T = temperature of reaction = $3652K$

Now put all the given values in the above formula, we get:

$\Delta G^o=(1684000J)-(3652K\times 543.7J/K)$

$\Delta G^o=-301592.4J=-301.59kJ$