Environmental and Industrial Chemistry: Pollution, Processes and Control
Core concepts
Environmental chemistry: understand the composition of the atmosphere, the greenhouse effect (CO₂, CH₄, N₂O, CFCs), ozone depletion by chlorine radicals, acid rain from SO₂ and NOₓ, photochemical smog from NOₓ and hydrocarbons, and water-quality parameters (BOD, COD, DO, pH, hardness). Know primary versus secondary pollutants and the difference between point and non-point sources. Control measures include scrubbers, catalytic converters, electrostatic precipitators and effluent treatment.
Industrial chemistry: focus on the major processes and their conditions. Contact process for H₂SO₄ (V₂O₅ catalyst, ~450 °C), Haber process for NH₃ (Fe catalyst, ~450 °C, 200 atm, with Le Chatelier reasoning about pressure and temperature), Ostwald process for HNO₃, Solvay process for Na₂CO₃, and the chlor-alkali process. Understand why conditions are chosen: compromise between equilibrium yield, rate and cost. Know the difference between calcination and roasting, and between wrought iron, steel and cast iron by carbon content.
Traps to watch
- Assuming lower temperature always improves an industrial process; rate matters too.
- Confusing BOD (biodegradable organic load) with COD (chemical oxidisable load).
- Forgetting that catalytic converters need stoichiometric air–fuel ratio to work efficiently.
- Mixing up the Solvay and Haber raw materials.
Worked example
Explain why the Haber process runs at about 450 °C although the reaction is exothermic. Lower temperature would increase equilibrium yield, but the rate would be impractically slow, so a compromise temperature with an iron catalyst is used; high pressure (~200 atm) shifts equilibrium towards ammonia because four moles of gas become two. Rule of thumb: industrial conditions balance thermodynamics, kinetics and economics.