For which formation is this spontaneous? (CHEM)?

Question

Use the Gibbs free energy equation shown below to determine the temperature range for which the formation of iron from rust is spontaneous.

ΔG = ΔH – TΔS

2Fe2O3(s) → 4Fe(s) + 3O2(g)

ΔH°f = 1648.4 kJ

ΔS°f = 549.6 J/K

Which is true:?

A. The reaction is spontaneous below 1648.4/0.5496 K.

B. The reaction is spontaneous above 1648.4/0.5496 K.

C. The reaction is always spontaneous.

D. The reaction is spontaneous below 1648.4/549.6 K.

E. The reaction is spontaneous above 1648.4/549.6 K.

Answer 1

we will solve for the temperature at which this is an equilibrium, (dG = 0)...

then we will find what to do with the temperature to make dG = "-" (spontaneous)

--------------------------

ΔG = ΔH – TΔS

0 = 1648.4 kJ - T(0.5496kJ/K)

T(0.5496 kJ/K) = 1648.4 kJ

T = 1648.4 kJ / 0.5496K  at this temp, dG = 0,... any higher, & ΔG = ΔH – TΔS,... will give a dG = "-" (spontaneous)

your answer is: A.The reaction is spontaneous below 1648.4/0.5496 K.