The chemical reaction that causes aluminum to corrode in air is given by: 4Al+3O
ID: 956502 • Letter: T
Question
The chemical reaction that causes aluminum to corrode in air is given by: 4Al+3O2?2Al2O3, in which at 298 K deltaHrxn = -3352 kJ and deltaSrxn = -625.1 J/K.
1) What is the standard Gibbs free energy for this reaction? Assume the commonly used standard reference temperature of 298 K.
Express your answer as an integer and include the appropriate units.
2) What is the Gibbs free energy for this reaction at 5975 K ? Assume that ?H and ?S do not change with temperature.
Express your answer to two decimal places and include the appropriate units.
3) At what temperature Teq do the forward and reverse corrosion reactions occur in equilibrium?
Express your answer as an integer and include the appropriate units.
Explanation / Answer
1)
?H = -3352.0 KJ
?S = -625.1 J/K
= -0.6251 KJ/K
T = 298 K
use:
?G = ?H - T*?S
?G = -3352.0 - 298.0 * -0.6251
?G = -3165.7202 KJ
Answer: -3166 KJ
2)
we have:
?H = -3352.0 KJ
?S = -625.1 J/K
= -0.6251 KJ/K
T = 5975 K
use:
?G = ?H - T*?S
?G = -3352.0 - 5975.0 * -0.6251
?G = 383 KJ
Answer: 383 KJ
3)
?G = 0.0 KJ (This is 0 at equilibrium)
?H = -3352.0 KJ
?S = -625.1 J/K
= -0.6251 KJ/K
use:
?G = ?H - T*?S
0.0 = -3352.0 - T *-0.6251
T = 5362 K
Answer: 5362 K
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