At what temperature, T eq, do the forward and reverse corrosion reactions occur
ID: 858218 • Letter: A
Question
At what temperature, Teq, do the forward and reverse corrosion reactions occur in equilibrium?
The chemical reaction that causes aluminum to corrode in air is given by
4Al+3O2?2Al2O3
in which at 298 K
?Srxn
= ?625.1 J/K
What is the standard Gibbs free energy for this reaction? Assume the commonly used standard reference temperature of 298 K?
What is the Gibbs free energy for this reaction at 5975K ? Assume that ?H and ?S do not change with temperature.
At what temperature, Teq, do the forward and reverse corrosion reactions occur in equilibrium?
?Hrxn? = ?3352 kJ?Srxn
= ?625.1 J/K
Explanation / Answer
1. DG = DH-TDS
= -3352 - 298*-625.1 = ?3165.7202 KJ
2. DG = DH-TDS
= -3352 - 5975*-625.1 = 382.9725 KJ
3. Given DH = -3352 kj DS = -625.1 j/k.
both DH,DS is -ve so that for spontaneou process T<DH/DS
T = 3352/0.625 = 5363.2 K
at 5363.2 K forward and reverse corrosion reactions occur in equilibrium.
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