Ammonia survives indefinitely in air. An agronomist studying how long ammonia survives in soil might need to know whether it survives because its oxidation is not spontaneous under ordinary conditions or whether the oxidation is spontaneous but just very slow. Calculate the standard Gibbs free energy of the reaction 4 NH₃(g) + 5O₂(g) → 4 NO(g) + 6 H₂O(g) and decide whether the reaction is spontaneous under standard conditions at 25°C.

PLAN Obtain the standard Gibbs free energies of formation from Appendix 2A, then use Eq. 8 to calculate the reaction Gibbs free energy.

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AG° = nAG₁° (products) - EnAG(reactants) (8)