Process thermochemistry: The neutralization of nitric acid by ammonia to form ammonium nitrate (NH4NO3) is best described as what type of reaction?

Introduction / Context:
Ammonium nitrate manufacture involves neutralizing nitric acid with ammonia to form an aqueous melt, which is then concentrated and solidified. Correctly identifying the thermic nature of the neutralization is essential for safe reactor design, heat recovery, and preventing runaway conditions, especially given the energetic nature of ammonium nitrate at high temperatures.

Given Data / Assumptions:

• Reactants: NH3 (typically gaseous) and HNO3 (aqueous).
• Product: NH4NO3 in solution; large heat release on neutralization.
• Industrial neutralizers incorporate heat removal.

Concept / Approach:
Acid–base neutralization reactions generally release heat. The specific reaction NH3 + HNO3 → NH4NO3 is strongly exothermic, and plants capture this heat in process water or generate low-pressure steam. The exothermicity is central to temperature control in neutralizers to avoid decomposition or undesirable side reactions in later steps.

Step-by-Step Solution:
Recognize acid–base neutralization → heat is released.Apply to NH3 + HNO3 → NH4NO3 with substantial enthalpy of neutralization.Therefore classify as “exothermic.”Design implication: incorporate cooling/heat recovery in neutralizer system.

Verification / Alternative check:
Plant heat balances show neutralizer duty recovered as hot process condensate or steam; operating manuals warn against inadequate cooling capacity.

Why Other Options Are Wrong:
Catalytic/autocatalytic: no catalyst is required for the neutralization step.Endothermic: contradicts measured heats of neutralization and plant practice.

Common Pitfalls:
Underestimating heat release, leading to temperature spikes that complicate downstream evaporation and increase safety risks.

Final Answer:
Exothermic