In industrial fertiliser manufacture, the reaction between liquid ammonia (NH3) and 60% nitric acid (HNO3) to produce ammonium nitrate (NH4NO3) is thermally characterized as which type of reaction?

Introduction / Context:
The neutralisation of nitric acid with anhydrous or aqueous ammonia to form ammonium nitrate is a key step in nitrogen fertiliser production. Correctly identifying the reaction heat effect is essential for safe reactor design, heat removal, and preventing runaway conditions in neutralisers and prilling/granulation units.

Given Data / Assumptions:

• Reactants: liquid NH3 and ~60% HNO3.
• Product: ammonium nitrate solution, NH4NO3(aq).
• Operation commonly carried out in well-cooled neutralisers.

Concept / Approach:
Acid–base neutralisation reactions typically release heat. The formation of ammonium nitrate from ammonia and nitric acid is strongly exothermic, demanding vigorous heat removal to control temperature and avoid excessive vapour generation and decomposition risks downstream.

Step-by-Step Solution:

Verification / Alternative check:
Plant heat balances show that substantial cooling duty is required during neutralisation, and neutraliser temperatures are tightly controlled to protect product quality and safety.

Why Other Options Are Wrong:

• Endothermic: contradicts observed heat release.
• Autocatalytic: the reaction does not require self-catalysis; it is a straightforward neutralisation.
• None of these or reversible only at very high pressure: irrelevant to this neutralisation step.

Common Pitfalls:
Confusing the safe neutralisation step with the thermal stability of concentrated ammonium nitrate; decomposition hazards are separate from the neutralisation exotherm.

Final Answer:
exothermic