Question

The chemical reaction that causes iron to corrode in air is given by 4Fe(s)+3O2(g)→2Fe2O3(s)

and

ΔrH∘ = −1684 kJ mol−1

ΔrS∘ = −543.7 J K−1 mol−1

a) What is the standard Gibbs energy change for this reaction? Assume the commonly used standard reference temperature of 298 K.

b) What is the Gibbs energy for this reaction at 3652 K ? Assume that ΔrH∘ and ΔrS∘ do not change with temperature.

c) The standard Gibbs energy change, ΔrG∘, applies only when the reactants and products are in their standard states. Assume that the above corrosion reaction is carried out in a flask where the reactants and products are in their standard states and the values of ΔrH∘ and ΔrS∘ do not change with temperature.

At what temperature, Teq, do the forward and reverse corrosion reactions occur in equilibrium?

Answer 1

dGo = dHo - TdSo is formula

a) dGo = - 1684 - ( 298)( -0.5437)                           ( dSo and dHo units must be same KJ)

             =   -1522 KJ /mol

b) dGo = -1684 -( 3652) ( -0.5437)

           = 301.6KJ/mol

c)   at equilibrium dGo = 0

hence dHo - TdSo = 0

dHo = TdSo

-1684 = Teq x ( -0.5437)

Teq = 3097.3 K