Thermochemistry of Haber–Bosch: The catalytic synthesis of ammonia from nitrogen and hydrogen is best described as which type of reaction?

Introduction / Context:
The Haber–Bosch process synthesizes ammonia by reacting nitrogen with hydrogen over an iron-based catalyst at high pressure. Its thermochemistry and reversibility govern operating choices such as temperature, pressure, and recycle, which together determine per-pass conversion and energy efficiency.

Given Data / Assumptions:

• Reaction: N2 + 3 H2 ⇌ 2 NH3.
• Standard enthalpy change is negative (heat released).
• Equilibrium is strongly dependent on temperature and pressure.

Concept / Approach:
The reaction is exothermic and reversible. Lower temperatures and higher pressures favour ammonia at equilibrium; however, low temperature slows the reaction rate, so industrial plants compromise at moderate temperatures with high pressures and extensive recycle. The reversibility is evident in the need to separate ammonia (via condensation/absorption) and recycle unconverted gases to drive overall yield upward.

Step-by-Step Solution:

Verification / Alternative check:
Plant data show heat removal between catalyst beds and use of waste heat for steam generation—typical for exothermic systems.

Why Other Options Are Wrong:

• Endothermic: contradicts the known heat release.
• Irreversible: kinetics allow both forward and reverse; equilibrium limits per-pass conversion.
• Neither exo/endothermic: incorrect for this reaction.

Common Pitfalls:
Confusing kinetic limitations with irreversibility; ignoring the reverse reaction significance when temperature rises.

Final Answer:
Exothermic and reversible