At 298 K, the standard Gibbs free energies of formation are
NO(g) = 86.6 kJ mol⁻¹ and NO₂(g) = 51.3 kJ mol⁻¹ (O₂(g) is zero).
Determine the standard Gibbs free energy change per mole of NO₂ produced for the reaction
2 NO(g) + O₂(g) → 2 NO₂(g).
Express your answer in kJ mol⁻¹ to the nearest kilojoule.