Question

What is the standard free energy change for the reaction below? Is the reaction expected to be spontaneous under standard conditions?

FeS(s) + O2(g) → Fe(s) + SO2(g)

Answer 1

Answer :

The standard free energy change for the reaction can be determined by considering the standard free energy changes of formation (∆G°_f) for each of the products and the reactants.

The standard free energy change of a reaction is :

The given reaction is :

The standard free energy changes of formation for each reactants and products are :

Compound	FeS(s)	O2(g)	Fe(s)	SO2(g)
∆G°f (kJ/mol)	-100.4	0.0	0.0	-300.2

Thus, the standard free energy change for the given reaction is =

Or, Thus, the free energy change for the above reaction is -199.8 kJ/mol

Now, we know for a spontaneous reaction, the free energy change of a reaction is negative .

And, for a non-spontaneous reaction, the free energy change of a reaction is positive.

As, for the above reaction the standard free energy change of the reaction is negative, thus it is spontaneous under standard conditions.