Question

Use the given data at 500 K to calculate ΔG°for the reaction 2H2S(g) + 3O2(g) →...

Use the given data at 500 K to calculate Δfor the reaction

2H2S(g) + 3O2(g) → 2H2O(g) + 2SO2(g)

Substance H2S(g) O2(g) H2O(g) SO2(g)
Δf(kJ/mol) -21 0 -242 -296.8
S°(J/K·mol) 206 205 189 248
0 0
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Answer #1

Solution:

The change in free energy (ΔG°) is calculated as,

ΔG° = ΔH° - T ΔS°

For the given reaction,

2H2S + 3O2 = 2H2O + 2SO2

ΔH° is calculated as,

ΔH° = (2 x ΔH°SO2 + 2 x ΔH°H2O) - (2 x ΔH°H2S - 3 x ΔH°O2)

= (2 mol x -296.8 kJ mol^-1 + 2 mol x -242 kJ mol^-1) - ( 2 mol x -21 kJ mol^-1 + 3 x 0 kJ mol-1) = -1035.6 kJ

ΔS° is calculated as,

ΔS° = (2 mol x S°SO2 + 2 mol x S°H2O) - ( 2 mol x S°H2S + 3 mol x S°O2)

= ( 2 mol x 248 JK-1 mol^-1 + 2 x 189 JK-1 mol^-1) - ( 2 x 206 JK-1 mol^-1 + 3 mol x 205 JK-1 mol^-1)

= -153 J K^-1= - 0.153 kJ K^-1

Therefore,

ΔG° = ΔH° - T ΔS°

= -1035.6 kJ - ( 500 K x - 0.153 kJ K-1)

= -1035.6 kJ  + 76.5 kJ

= -959.1 kJ

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