Nitric acid: the Ostwald process (NH3 -> NO -> NO2 -> HNO3)

The three-stage industrial route to nitric acid, each stage a genuinely different reaction regime. First a catalytic burner oxidizes ammonia in air over a Pt-Rh gauze (4 NH3 + 5 O2 -> 4 NO + 6 H2O) — this is a KINETICALLY selective step, not an equilibrium one: thermodynamics actually favours N2, and only the short contact time on the hot catalyst steers it to nitric oxide, so it's modeled as a fixed-conversion reactor (a Gibbs-minimization reactor here would wrongly predict N2). The gas is cooled and the nitric oxide is oxidized to nitrogen dioxide (2 NO + O2 -> 2 NO2), an exothermic step favoured by the low temperature. Finally the NO2 is absorbed in water to form nitric acid (3 NO2 + H2O -> 2 HNO3 + NO) — modeled as NO2 + water capture into the acid liquor. Cited heats of reaction (NH3 oxidation -226.3 kJ/mol NH3; NO oxidation -57.0 kJ/mol NO). Honesty notes: the burner and NO-oxidation conversions are fixed (representative values), not solved from kinetics; the water-absorption tower is a capture simplification (the acid-forming reaction and HNO3 solution non-ideality are not modeled), the same posture the sulfuric-acid and carbon-capture examples use. The point is the contrast — one kinetically-controlled step next to two thermodynamically-favoured ones — which is exactly why a nitric-acid plant can't be modeled with equilibrium reactors throughout.