Question

The chemical reaction that causes iron to corrode in air is given by

4Fe+3O2→2Fe2O3

in which at 298 K

ΔH∘rxn	= −1684 kJ
ΔS∘rxn	= −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 ΔH and ΔS do not change with temperature.

Part C:

At what temperature Teq do the forward and reverse corrosion reactions occur in equilibrium?

Answer 1

A)

ΔH = -1684.0 KJ

ΔS = -543.7 J/K

= -0.5437 KJ/K

T = 298 K

use:

ΔG = ΔH - T*ΔS

ΔG = -1684.0 - 298.0 * -0.5437

ΔG = -1521.9774 KJ

Answer: -1522 KJ

B)

Now we have:

ΔH = -1684.0 KJ

ΔS = -543.7 J/K

= -0.5437 KJ/K

T = 3652 K

use:

ΔG = ΔH - T*ΔS

ΔG = -1684.0 - 3652.0 * -0.5437

ΔG = 302 KJ

Answer: 302 KJ

C)

ΔG = 0.0 KJ (because this is equilibrium)

ΔH = -1684.0 KJ

ΔS = -543.7 J/K

= -0.5437 KJ/K

use:

ΔG = ΔH - T*ΔS

0.0 = -1684.0 - T *-0.5437

T = 3097 K

Answer: 3097 K