Formula: (NH₄)₂SO₄
Derivation:
1. NH₄⁺ has +1 charge
2. SO₄^2- has -2 charge
3. Need 2 ammonium ions to balance 1 sulfate ion
4. Molecular weight: 132 g/mol (N=14, H=1, S=32, O=16)
5. Common agricultural fertilizer (21% N, 24% S)

Essential roles:
1. Nitrogen (N): Protein/DNA synthesis, chlorophyll production (leaf growth)
2. Phosphorus (P): ATP/ADP energy transfer, root development
3. Potassium (K): Enzyme activation, water regulation (stomata control)
Agricultural benefits:
– Replenishes soil nutrients depleted by crops
– Increases yield and crop quality
– NPK ratio tailored to specific crops (e.g., 10-10-10 balanced)

Thermodynamic reasons:
1. Equilibrium compromise: N₂ + 3H₂ ⇌ 2NH₃ (exothermic)
2. Lower temperatures favor product (Le Chatelier) but slow reaction
3. 450°C balances reasonable yield (15-20%) with practical reaction rate
4. 800°C would shift equilibrium left (≤5% yield) despite faster kinetics

Kinetic reasons:
1. Activation energy: N≡N triple bond requires high energy to break
2. 200°C gives <1% yield due to extremely slow reaction
3. Catalyst (iron) needs ≥400°C for optimal activity
4. Compromise between rate (favors higher T) and equilibrium (favors lower T)
5. Industrial reality: Better to recycle unreacted gases than wait for slow reaction

Iron’s role:
1. Heterogeneous catalyst – provides surface for reaction
2. Lowers activation energy by weakening N≡N bond
3. Promoted with K₂O/Al₂O₃ to increase efficiency
4. Typical composition: 90-95% Fe₃O₄ with additives
5. Lasts 5-10 years before replacement needed