Answer to Question #334283 in General Chemistry for Sofia

Question

Calculate the standard free-energy change for the reaction at 25 ∘C.

Refer to the list of standard reduction potentials.

2Au3+(aq)+3Mg(s)↽−−⇀2Au(s)+3Mg2+(aq)

Δ𝐺∘= kJ

Answer 1

The reduction half cell reactions and E⁰ values are:

Au³⁺(aq) + 3e →Au (s)   E⁰ = + 1.52 V 

Mg(s) - 2e  → Mg²⁺(aq) E⁰ = -2.36 V 

In the reaction, Au is being oxidized and so the overall cell potential is:

E⁰ = ((-2.36) – (+1.52)) V = -3.88 V

The reaction involves 6 electrons so, using ΔG⁰ = -nFE⁰: 

ΔG⁰ = - (6) × (96485 C mol^-1) × (-3.88 V) =2246171 J mol^-1 = 2.25 × 10³ kJ mol^-1