Question

The chemical reaction that causes magnesium to corrode in air is given by 2Mg+O2→2MgO in which at 298 K ΔH∘rxn = −1204 kJ ΔS∘rxn = −217.1 J/K

Part A 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.

Part B

What is the Gibbs free energy for this reaction at 5958 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 = -1204.0 KJ

ΔS = -217.1 J/K

= -0.2171 KJ/K

T = 298 K

use:

ΔG = ΔH - T*ΔS

ΔG = -1204.0 - 298.0 * -0.2171

ΔG = -1139.3042 KJ

Answer: -1139 KJ

b)

Now we have:

ΔH = -1204.0 KJ

ΔS = -217.1 J/K

= -0.2171 KJ/K

T = 5958 K

use:

ΔG = ΔH - T*ΔS

ΔG = -1204.0 - 5958.0 * -0.2171

ΔG = 89.5 KJ

Answer: 89.5 KJ

c)

Now we have:

ΔH = -1204.0 KJ

ΔS = -217.1 J/K

= -0.2171 KJ/K

ΔG = 0 for equilibrium process

use:

ΔG = ΔH - T*ΔS

0.0 = -1204.0 - T *-0.2171

T = 5545.8314 K

Answer: 5546 K