Haber-Bosch Ammonia Synthesis & NPK Fertilizers

Haber-Bosch Reactor

N₂ + 3H₂ ⇌ 2NH₃
ΔH° = −92.4 kJ/mol (exothermic)

Temperature 450 °C

Pressure 200 atm

Reactor state

Equilibrium yield

–

Live conversion

–

NH₃ formed

Reaction rate

–

How it works

N₂'s triple bond (N≡N, ≈945 kJ/mol) is one of the strongest covalent bonds known — nitrogen gas is inert at room temperature because breaking it takes so much energy. The iron catalyst provides a surface where N₂ and H₂ can adsorb and dissociate at far lower energy cost than in the gas phase, but industrial rates still need ≈400–500 °C and ≈150–300 atm.

Pressure ↑ — shifts equilibrium toward NH₃ (Le Chatelier: 4 mol of gas → 2 mol, so higher pressure favors the side with fewer moles).
Temperature ↑ — speeds up the reaction (faster kinetics) but lowers the equilibrium yield, because the forward reaction is exothermic.
Real plants run a compromise: hot enough to react in seconds, with a catalyst to compensate for the lower equilibrium at that temperature, then recycle unreacted gas.

Fritz Haber and Carl Bosch won Nobel Prizes for turning atmospheric nitrogen into ammonia at industrial scale — the process that made synthetic fertilizer, and roughly half of today's global food supply, possible ("bread from air").

Molecules fall onto the iron catalyst bed. When N≡N breaks and 3 H atoms are available, NH₃ forms and rises to the outlet.

Nitrogen (N) Hydrogen (H) Ammonia (NH₃) Fe catalyst bed

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Equilibrium yield vs. pressure

Curve shows the approximate NH₃ equilibrium mole-fraction at the current temperature as pressure varies (illustrative industrial trend, not a rigorous Gibbs-energy calculation). The dot marks your current temperature/pressure setting.

NH₃ → NPK fertilizers

Urea CO(NH₂)₂ 46-0-0

Ammonium nitrate NH₄NO₃ 34-0-0

Typical NPK blend 20-10-10

N — from this NH₃ P — phosphate rock K — potash

Numbers are the label N-P-K percentages by weight. This reactor only supplies the nitrogen (N) leg of the triad — ammonia is oxidized to nitric acid or reacted with CO₂/acids to make urea and ammonium nitrate; phosphorus and potassium in a blended fertilizer come from mined phosphate rock and potash, not from Haber-Bosch.