Thermochemistry check:\nThe oxidation of ammonia (as in the Ostwald process for nitric acid) is fundamentally ________.

Introduction / Context:
Oxidation of ammonia to nitric oxide is the first step of the Ostwald process for nitric acid, a cornerstone of nitrogen fertilizer production. The thermochemistry—whether the reaction releases or absorbs heat—controls reactor design, temperature profiles, and heat recovery schemes.

Given Data / Assumptions:

• Main reaction: 4 NH3 + 5 O2 → 4 NO + 6 H2O (with platinum-group catalyst).
• Industrial operation uses gauze catalysts at high temperatures (∼800–900 °C).
• We focus on thermal character, not side reactions.

Concept / Approach:
The oxidation of ammonia is strongly exothermic, liberating substantial heat that sustains high catalyst temperatures after light-off and enables waste-heat recovery (e.g., raising steam). While the process is catalytic (Pt-Rh gauzes), the core thermochemical identity is exothermicity, not endothermic or autocatalytic behavior.

Step-by-Step Solution:
Consider bond energies: oxidation of a reduced nitrogen species to NO/H2O releases heat.Observe practice: after ignition, the bed remains hot due to the exotherm and gas preheating.Therefore, classify the reaction as exothermic.

Verification / Alternative check:
Plant heat balances show significant heat recovery from converter effluent; this would be impossible for an endothermic reaction without external energy input.

Why Other Options Are Wrong:
Endothermic contradicts the known heat release; “non-catalytic” is false—Pt gauze is required; “autocatalytic” is not the standard description; “athermal” is incorrect.

Common Pitfalls:
Confusing high operating temperature with endothermicity; the bed is hot because the reaction releases heat and the catalyst must withstand it.

Final Answer:
exothermic