Haber Process — the NEET Chemistry reaction: mechanism, reagents, conditions, structures and exam traps.
Haber Process The Haber–Bosch process synthesizes ammonia by the reversible, exothermic reaction of dinitrogen and dihydrogen over a promoted iron catalyst at high pressure and moderately high temperature. The reaction is conducted in a recycle loop where ammonia is condensed out to drive equilibrium forward and unreacted gases are returned to the converter. Colorless gases are fed; reactor runs hot due to exothermicity. Downstream cooling condenses colorless liquid ammonia with a sharp, pungent odor; it turns moist red litmus blue and fumes in air. Exothermic with ( H 298 -92.4 , kJ ,mol -1 ) per 2 mol NH3 formed; equilibrium is favored by high pressure and low temperature. The reaction is reversible; industrial operation uses a compromise temperature and continuous NH3 removal to drive conversion. 1. Adsorption: N2(g) and H2(g) are physically and then chemisorbed onto the Fe surface; H2 dissociates readily to adsorbed H atoms (H ). 2. N≡N activation (rate-determining): Electron-rich Fe sites (promoted by K2O) weaken and dissociate N2 to surface N atoms: ( N 2(g) [Fe] adsorption N 2 [] activation 2 ,N ). 3. Stepwise surface hydrogenation: Sequential addition of H to N forms NH , then NH2 , then NH3 : (N + H NH ); (NH + H NH 2 ); (NH 2 + H NH 3 ). 4. Desorption: Formed NH3 desorbs from the surface to the gas phase: (NH 3 NH 3(g) ), regenerating active sites. 5. Equilibrium management: Because ( n gas = -2 ) and the reaction is exothermic, high pressure and lower temperature favor NH3; industrially a compromise (≈673 K, ≈200 atm) balances rate and yield. Continuous removal of NH3 by cooling/condensation shifts equilibrium forward (Le Ch a telier). 6. Catalyst stabilization: Al2O3 (and sometimes CaO) acts as a structural promoter to improve mechanical strength and surface area retention; K2O enhances electron density at Fe, facilitating N2 dissociation. Assuming very high temperature increases yield — exothermic reaction actually favors lower T; 673 K is a compromise for rate. Misstating the catalyst/promoters — NCERT: finely divided Fe with K2O and Al2O3 promoters (not Pt/Pd/Ru; do not default to Mo in NCERT context). Forgetting the 1:3 stoichiometric ratio (N2:H2) and that catalyst does not change equilibrium position, only rate.