Non-metals, environmental and industrial chemistry
Non-metals, environmental and industrial chemistry tests key non-metals, the Haber and Contact processes and pollution.
Key non-metals
Oxygen supports combustion and is tested by relighting a glowing splint. Hydrogen burns with a squeaky pop. Carbon dioxide turns limewater milky. Chlorine is a pale green gas that bleaches damp litmus and kills bacteria in water treatment. Nitrogen is unreactive because of its strong triple bond. Sulfur burns in oxygen to form sulfur dioxide.
Industrial processes
The Haber process makes ammonia: N2 + 3H2 ⇌ 2NH3, using an iron catalyst at about 450 °C and 200 atm. Ammonia is used for fertilisers. The Contact process makes sulfuric acid: sulfur is burned to SO2, then SO2 + O2 ⇌ SO3 with a vanadium(V) oxide catalyst at about 450 °C, followed by absorption in concentrated sulfuric acid. Limestone (calcium carbonate) is heated to make quicklime and is used to neutralise acidic soil and flue gases.
Environmental chemistry
Carbon dioxide and methane are greenhouse gases. Carbon monoxide is toxic because it binds to haemoglobin. Sulfur dioxide and nitrogen oxides dissolve in rain to form acid rain, damaging buildings, soils and lakes. Particulates from incomplete combustion harm lungs. Chlorine in water treatment controls pathogens but can form harmful by-products.
Worked example
The Haber process uses a moderate temperature of about 450 °C even though low temperature favours the exothermic forward reaction. Reasoning: at very low temperature the yield is higher but the rate is far too slow. The iron catalyst works best at around 450 °C, so the conditions are a compromise between yield and rate. High pressure shifts the equilibrium towards fewer gas molecules, increasing ammonia yield.
Traps
A catalyst does not increase equilibrium yield; it only helps the system reach equilibrium faster. Carbon dioxide is not the only greenhouse gas. Chlorine does not clean water by removing dirt; it disinfects by killing microorganisms. Nitrogen is unreactive because its triple bond is strong, not because it is a noble gas.