Using G^o_f (HI) = 1.3 kJ/mole, calculate the standard free energy change for the following reaction,

${\displaystyle H_2\left(g\right)+I_2\left(g\right)\to 2HI\left(g\right)}$

To find the standard free energy change (ΔG°) for the reaction

$H_2\left(g\right)+I_2\left(g\right)\to 2HI\left(g\right)$

we use the formula:

ΔG° = Σ G°_f(products) – Σ G°_f(reactants)

Given data:

G°_f(HI, g) = 1.3 kJ mol^–1

For elements in their standard states, the standard free energy of formation is zero:

G°_f(H₂, g) = 0

G°_f(I₂, g) = 0

Now calculate the sum for the products:

Σ G°_f(products) = 2 × G°_f(HI) = 2 × 1.3 kJ mol^–1 = 2.6 kJ mol^–1

And the sum for the reactants:

Σ G°_f(reactants) = G°_f(H₂) + G°_f(I₂) = 0 + 0 = 0

Finally, the standard free energy change is:

ΔG° = 2.6 kJ mol^–1 – 0 = 2.6 kJ mol^–1